Log Message:
net/unison2.48: Remove (as not useful given wire protocol breaks)

As proposed on pkgsrc-users with no comments, and concurrence by wiz@
with my analysis that this cannot work to interoperate with old
software.  Note that unison has multiple versions only to deal with
wire protocol breaks that happen every version; without that there
would just be a single recent unison version.

In addition to being old and unused, I believe that 2.48 from pkgsrc
(built now with pkgsrc's ocaml) cannot work to interoperate with other
systems that still have 2.48, because pkgsrc's ocaml version has an
incompatible serialization format, and the unison wire protocol is
effectively the combination of the unison version and the ocaml
serialization version.

(Separate from 2.32 and 2.40 removal to ease separate reverting,
should it be necessary.)