binutils 2.20: remove source files

binutils 2.20: remove source files

Binutils 2.20 has not been building for a month, but the source files
were still present in case we wanted to switch it back on.

Per IRC discussion, the general consensus is that DragonFly wants to
continue to maintain two sets of binutils in addition to two compilers.
A new vendor branch has been created, vendor/BINUTILS-ALL, and
binutils 2.20 is the first version to go into this branch.  All future
versions of binutils will also go into this branch rather than create
a new vendor branch each time.  Everything else including objformat
and the naming scheme will remain as it was.  The idea is that the
newest version of binutils is always "prime" and the older version is
the backup which does not require updating.  When a new version of
binutils is brought in, the previous backup version will be deleted.
That's what is happening with binutils version 2.20 today.