Remove SkFallbackAlloc and SkFixedAlloc.

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Debug-ASAN;skia.primary:Test-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Debug-MSAN

TBR=reed@google.com

Change-Id: I1000dc9ed8ad65b249798759d9af99f47fc237d2
Reviewed-on: https://skia-review.googlesource.com/6809
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Herb Derby <herb@google.com>
25 files changed