remove unused OpenGL function
remove unused OpenGL function

halide_opengl_init_kernels was an identical-but-unused duplicate of
halide_opengl_initialize_kernels.


Former-commit-id: ea0ed93ac81520f8dd0278fbc644755f94cd2dbc
darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide