Implement SQLitePersistentSharedDictionaryStore::ClearDictionaries

This method will be called from BrowsingDataRemover.

Bug: 1413922
Change-Id: I689bbbd96fb95be5efc39369d01711a4ea80e8fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4563600


Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Reviewed-by: Patrick Meenan <pmeenan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1149418}