x/ref: Move x/ref/lib/flags/buildinfo to x/lib/buildinfo

This reduces package nesting, and is also nicer since the
devtools/v23 tool uses this mechanism, and it's better for v23 to
have absolutely no dependencies on x/ref/...

MultiPart: 2/3
Change-Id: Ifee7aa2443e0b71852a7f03cca1d690628ba75c0
6 files changed