Clean Up src/parsers
State: closed

Looking at this in detail noticed quite a few unused functions and pre-processor directives. There was also a mismatch in types between the .pyx and C structs

Labels:
name: IO Data
description: IO issues that don't fit into a more specific label
name: Clean

Comments:
lgtm ping on green.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=h1) Report
> Merging [#26445](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/7ee26a8223b7a9a1370246d8420052a2101ed12e?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26445/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26445      +/-   ##
==========================================
- Coverage   91.73%   91.72%   -0.01%     
==========================================
  Files         174      174              
  Lines       50754    50754              
==========================================
- Hits        46560    46556       -4     
- Misses       4194     4198       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.23% <ø> (ø)` | :arrow_up: |
| #single | `41.69% <ø> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26445/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `78.94% <0%> (-10.53%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26445/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.02% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=footer). Last update [7ee26a8...9d5f110](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=h1) Report
> Merging [#26445](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/7ee26a8223b7a9a1370246d8420052a2101ed12e?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26445/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26445      +/-   ##
==========================================
- Coverage   91.73%   91.72%   -0.01%     
==========================================
  Files         174      174              
  Lines       50754    50754              
==========================================
- Hits        46560    46556       -4     
- Misses       4194     4198       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.23% <ø> (ø)` | :arrow_up: |
| #single | `41.69% <ø> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26445/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `78.94% <0%> (-10.53%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26445/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.02% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=footer). Last update [7ee26a8...9d5f110](https://codecov.io/gh/pandas-dev/pandas/pull/26445?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

@jreback all green
thanks