pmb.aportgen.binutils: fix for new binutils file conflict

Newly generated binutils package has file conflicsts with non-cross binutils.

  ERROR: binutils-2.37-r3: trying to overwrite usr/lib/bfd-plugins/libdep.so
         owned by binutils-aarch64-2.37-r3.

See also https://builds.sr.ht/~postmarketos/job/597030#task-pmbootstrap_build

Fix the generator to produce package that does not include these plugins.

Related: pmaports@23b6654f