It's been unused for nearly 9 years. By the end of the series stdvga.c's
sole purpose will be to make sure VRAM writes use the bufio ioreq path.

1: properly reject "indirect" VRAM writes
2: drop stdvga's "stdvga" struct member
3: remove unused MMIO handling code
4: drop stdvga's "gr[]" struct member
5: drop stdvga's "sr[]" struct member
6: drop stdvga's "{g,s}r_index" struct members
7: drop stdvga's "vram_page[]" struct member
8: drop stdvga's "lock" struct member
9: drop .complete hook for intercept handling

Jan