BuildClassBoilerplate accessed the native context to get the
class_function_descriptors. Baseline compilation should be native context
independent, so we shouldn't access the native context at all. As it happens,
class_function_descriptors wasn't used so can just be removed.

BUG=chromium:898076, v8:8041

Change-Id: If9c0edf3dfde68c76ea87820f9d4b080aac6d60e
Reviewed-on: https://chromium-review.googlesource.com/c/1298033Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56958}