x/lib: 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: 1/3
Change-Id: Ia65484a884793c721324e3169f23331a5e4fe298
1 file changed