Remove the partial-flush machinery from GrResourceAllocator

Since review.skia.org/366716 this is unused and it makes our life
a whole lot simpler. And a little faster.

Bug: skia:10877
Change-Id: Ib7205bae57ce282f0e4f33c7c780a4c3e5159ea5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/369436
Commit-Queue: Adlai Holler <adlai@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
5 files changed