Remove redundant field pr_sctp_on.

MFC after: 1 week
Remove our hacked GNU patch.

The old (2.1) GNU patch has outlived its days.  The major
local changes have been moved into the less restrictedly
licensed patch(1) we adopted in usr.bin/ .

A much newer version of GNU patch is available in the
ports tree (devel/patch).

Disconnect from the build and remove.