PERF: perf issue with dropna on frame

took out the apply on ``count`` and just compute directly

```
-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------
frame_dropna_axis1_any                       | 147.5154 | 334.2137 |   0.4414 |
frame_dropna_axis1_all                       | 251.1443 | 437.9021 |   0.5735 |
frame_dropna_axis0_all                       |  80.6900 |  80.8613 |   0.9979 |
frame_dropna_axis0_any                       |  58.6040 |  54.6887 |   1.0716 |
-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------

Ratio < 1.0 means the target commit is faster then the baseline.
Seed used: 1234

Target [c6e300d] : PERF: perf issue with dropna on frame
Base   [5e176a9] : Merge pull request #5738 from y-p/PR_json_pr_ver

BLD: ci/print_versions.py learned to output json

```