[Viz] Remove unused TestContextProvider::Create() variant

Helps clarify the work needed to eliminate TestContextProvider using
RasterImplementationGLES.

Bug: 40194377
Change-Id: I48bd5ddbbaaa65159f732be501d260f949185fa0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5613430


Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312685}