There is always only one display that can be associated with a context,
so get*Current*Display is confusing.

Bug: None
Change-Id: Iff3a9fc5ad1154b046bb30d7f46a468802ba7fcc
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1558958Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>