Remove obsolete SkWuffsCodec WhichDecoder enum
Remove obsolete SkWuffsCodec WhichDecoder enum

This 1-element enum has been obsolete since December 2020
(https://skia-review.googlesource.com/c/skia/+/342836 "Have SkWuffsCodec
use one Wuffs decoder").

Bug: skia:8235
Change-Id: I679222d7e0500902ff6e7a1c5569695a93be0060
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/498136
Auto-Submit: Nigel Tao <58ae08b3356928ff9c67562b4719487d54fe8348@google.com>
Reviewed-by: Leon Scroggins <995cad867ca30d6399abe011583a53547c8afea1@google.com>
Commit-Queue: Leon Scroggins <995cad867ca30d6399abe011583a53547c8afea1@google.com>

aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia