This reverts commit f5c89c1a6f.
Reason for revert:
Bootstrapping doesn't work because the index doesn't give us
all changes. In addition, we would have to filter way more
refs with this cache because the index-backed cache limitted
the ref filtering by recency (= you can't fetch a change from
say 2015) which is another performance bottleneck.
Change-Id: I447eaeb652e530ed560f31de15bb012912e14fff
ace3dc9f0a