Mark Runtime::kInlineGeneratorGetContext as not needing a FrameState
(matching the other Generator field-loading intrinsics) and avoid
a call to PrepareEagerCheckpoint() in VisitResumeGenerator() (since
there should never be a deopt during resume).

Change-Id: I03a2d89914bc7de27bbfe6228ca115e635ea4c4e
Reviewed-on: https://chromium-review.googlesource.com/506815Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45382}