More teacher related cleanup in Glanceables

This includes:
- `GlanceablesV2ClassroomTeacherView` flag,
- unused OAuth2 scopes,
- `GlanceablesClassroomClientImpl::InvokeOnceTeacherDataFetched`,
- `GlanceablesClassroomClientImpl::OnTeacherDataFetched`,
- `GlanceablesClassroomClientImpl::GetFilteredTeacherAssignments`,
- unused histograms.

OBSOLETE_HISTOGRAMS=These histograms and associated code were not used in production.

Bug: b/333576791
Change-Id: I625be012b0c97f284eb3aaf10d1feca60ba86a52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5431515
Reviewed-by: Michele Fan <michelefan@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Commit-Queue: Artsiom Mitrokhin <amitrokhin@chromium.org>
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1285097}
NOKEYCHECK=True
GitOrigin-RevId: 703febe5fb7d4f0cda985ab089a6b2f795bee43a
2 files changed