Fix GLES2 negative texture api tests.

Fix GLES2 negative texture api tests.

- Remove broken compressedtexsubimage2d_invalid_format test. Function is not
  required to generate INVALID_ENUM on invalid format. Spec only states that
  format must match the target texture format or INVALID_OPERATION.
- Remove broken generatemipmap_invalid_target_bind test.
- Add npot extension check to generatemipmap_npot_wdt_hgt test.
- Add GL_EXT_texture_compression_s3tc and GL_IMG_texture_compression_pvrtc
  format pretty-printing.

Bug: 18770284
Change-Id: I9c2c8d059b04eb51885062e9f0b78c2254050521