Don't cast emscripten pointers when assembling WebGL interface

Since we are now referencing the exact methods instead of calling
GetProcAddress, there is no need to cast the function pointers. This
also catches a bug where the emscripten signatures for glWaitSync and
glClientWaitSync did not match the OpenGL API.

Change-Id: If365a8f6090961cb4b44146d87e102430bc5b30f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/320659
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
2 files changed