TEST: Fix test/recipes/15-test_rsa.t

Perl strings should be compared with 'eq', not '=='.
This only generates a perl warning, so wasn't immediately noticed.

Also, remove the check of disabled 'dsa'.  That never made reak sense.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/13645)

test/recipes/15-test_rsa.t

@@ -49,7 +49,7 @@ sub run_rsa_tests {
 
      SKIP: {
          skip "Skipping msblob conversion test", 1
-	     if disabled($cmd) || disabled("dsa") || $cmd == 'pkey';
+	     if disabled($cmd) || $cmd eq 'pkey';
 
          subtest "$cmd conversions -- public key" => sub {
 	     tconversion( -type => 'msb', -prefix => "$cmd-msb-pub",