SimpleCache: audit M85-expiring histograms (3/???)

IndexWriteToDiskTime.* --- remove
IndexWriteInterval.* --- remove
IndexWriteReason* -- keep, relevant to outdated index issue some
IndexRestoreTime --- keep, relevant for CacheStorage-style use
IndexNumEntriesOnWrite --- keep, just used in a study
IndexInitializeMethod --- keep, relevant to index freshness
IndexInitializationWaiters --- remove, not very interesting
IndexFileStateOnLoad -- keep, index freshness
IndexEntriesLoaded, Restored --- remove, NumEntriesOnWrite has size.
IndexCorrupt --- remove, or rather wasn't there in first place.
IndexCreatedEntryCount --- keep, index freshness

Fixed: 1089945, 1089944, 1089943
Fixed: 1089942, 1089941, 1089940
Fixed: 1089939, 1089938, 1089937
Fixed: 1089936, 1089935, 1089934
Fixed: 1089933, 1089932, 1089931
Fixed: 1089930, 1089928, 1089927
Fixed: 1089926, 1089925, 1089924
Fixed: 1089923, 1089922, 1089921
Change-Id: I2e7aa493692e8d128dab3cde0e4c74aec0947734
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2261171
Reviewed-by: Ben Kelly <wanderview@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Maksim Orlovich <morlovich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#782441}