gpg: Remove options --pgp2 and --rfc1991.

* g10/gpg.c (oRFC1991, oPGP2): Remove
(opts): Remove --pgp2 and --rfc1991.
* g10/options.h (CO_PGP2, CO_RFC1991): Remove.  Remove all users.
(RFC2440, PGP2): Remove.  Remove all code only enabled by these
conditions.
* tests/openpgp/clearsig.test: Remove --rfc1991 test.
--

The use of PGP 2.c is considered insecure for quite some time
now (e.g. due to the use of MD5).  Thus we remove all support for
_creating_ PGP 2 compatible messages.

tests/openpgp/clearsig.test

@@ -23,17 +23,6 @@ for i in $plain_files plain-large ; do
 done
 
 
-# ======================================
-# and once more to check rfc1991
-# ======================================
-
-if have_pubkey_algo "RSA"; then
-  for i in $plain_files plain-large ; do
-      $GPG -u $usrname3 --rfc1991 --digest-algo md5 --clearsign -o x --yes $i
-      $GPG --verify x
-  done
-fi
-
 # ======================================
 # and one with long lines
 # ======================================
@@ -100,7 +89,7 @@ cat >y <<EOF
 	    }
 	    /* ask for file and hash it */
 -	    if( c->sigs_only ) {
-+	    if( c->sigs_only )   
++	    if( c->sigs_only )
 		rc = hash_datafiles( c->mfx.md, NULL,
 				     c->signed_data, c->sigfilename,
 			n1? (n1->pkt->pkt.onepass_sig->sig_class == 0x01):0 );