Remove unused IFontManager#updateFontFile().

The caller was removed in
commit 3de07491
This CL also does some cleanup:
- Extract OtfFontFileParser to a separate file.
- Remove boilerplate in UpdatableFontDirTest.

Bug: 187879195
Test: m -j
Test: atest FrameworksServicesTests:UpdatableFontDirTest
Change-Id: Id3e369222c35f550c6d53e8649ab07647701c070