This reverts commit cdd1ff41.

It turns out it’s more pain to disable libsocialweb and try to fight the
irrepressible combination of automake and Vala than it is to just
un-break libsocialweb to get distcheck to pass. Turns out that it’s
basically impossible to stop automake trying to generate C files from
.vala files, even if those .vala files are listed in EXTRA_DIST and not
SOURCES, or are hidden behind an if ENABLE_LIBSOCIALWEB.