[Android] make_apk: Make the code handling icons easier to read.

`customize.py` is horrible to read, and `CustomizeIconByDict()` is one
of the biggest offenders.

The first two commits does some clean-up that allows us to get rid of
some checks or moves them to an earlier stage in make_apk.

The last commit rewrites `CustomizeIconByDict()` to make it easier to
follow, mostly by getting rid of `drawable_dict` and all the attempts to
be smart by over-manipulating it.
> Do you mean moving GetIconSizeName() to manifest_parser_json.py and doing this kind of processing earlier?

Maybe not as early as in manifest_parser_json.py, but in make_apk.py before going into customize. Basic idea is
```
size_icon_map = parser.icons()
size_name_icon_map = MapSizeToSizeName(size_icon_map)
if options.icon:
  size_name_icon_map['default'] = options.icon
app_info.icon = size_name_icon_map
Customize(app_info)
```