[RFC] Removing support for GCJ and GCJFLAGS from dpkg?

Hi!

While going through the supported compilers and build flags recently,
I noticed that dpkg-buildflags and the various dpkg Makefile fragment
files still have support for gcj, but that compiler seems to have
stopped being maintained some time ago. According to Wikipedia
(<https://en.wikipedia.org/wiki/GNU_Compiler_for_Java>) the final
release was in 2018, and we do not even have it in Debian anymore.

So I guess it should be fine to rip that off? A quick codesearch.d.n
didn't reveal much of a usage. But I'd like to hear whether this would
break or disrupt things, before I consider removing these.

Thanks,
Guillem