See GPU_matrix.h & gpu_matrix.c for the important changes. Other files are mostly just updated to use the latest API.
- remove unused functions, defines, enums, comments
- remove "3D" from function names
- init to Identity transform (otherwise empty stack)
- gpuMatrixReset lets outside code return to initial state
Part of T49450
Follow up to D2626 and 49fc9cff3b