Cleanup GLES2Decoder::Initialize

* DisallowedFeatures are always default constructed.
* Checking for gpu rasterization is not very useful. No clients would
  request it and there is no way to send any raster requests to gles
  decoder.
* Only two fields are needed -- context_type and
  lose_context_when_out_of_memory.

Bug: 441427746
Change-Id: I11693c921131f06228ceae33f4f39f0afbd2be32
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6917518
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Reviewed-by: Kyle Charbonneau <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1512546}