Simplify function names in opengl.cpp
Simplify function names in opengl.cpp

Now that everything lives in Halide::Runtime::Internal, there is no need for
long function prefixes anymore.


Former-commit-id: 19acdc7cf3944494cc4949aefda3385f7a9ad7cb
darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide