Deletes header files and BUILD targets for SpdyUnsafeArena, which is no longer used.
gfe-relnote: n/a (deletes unused code/BUILD targets)
PiperOrigin-RevId: 284816046
Change-Id: I69f074a61077fc8396448c2524ea5387c57a46ab
QUICHE (QUIC, Http/2, Etc) is Google‘s implementation of QUIC and related protocols. It powers Chromium as well as Google’s QUIC servers and some other projects.