Stop supporting VC8 (Visual Studio 2005) in GrConfig

Bug: skia:
Change-Id: I5d447ea40ef541682f1e855d14e07bf8e45ee89a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/203392
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
1 file changed