Get rid of glGetError() calls in GLES2 renderer.

It's not usually useful, and it causes pipeline stalls.

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extra : rebase_source : fb1b9b3ffdee2a41fdaee5d30e7f218eacb2eaaa
SDLK_DELETE should probably be SDLK_BACKSPACE on iOS.

The key on the software keyboard works like backspace, at least. Not sure
 what happens with a bluetooth keyboard here.

--HG--
extra : rebase_source : 9db0fb0ccf78490db0443e975a55344a39416954