Remove references to IsNewAvatarMenu since the flag was removed.

This CL removes all references of the new-avatar-menu flag since it's
no longer used. The new avatar menu is always shown on desktop and never
on Mobile and ChromeOS.

BUG=517582

Review URL: https://codereview.chromium.org/1307093004

Cr-Commit-Position: refs/heads/master@{#352041}
48 files changed