mk-ca-bundle.pl: make -u delete certdata.txt if found not changed

certdata.txt should be deleted also when the process is interrupted by
"same certificate downloaded, exiting"

The certdata.txt is currently kept on disk even if you give the -u
option

Closes #2655

lib/mk-ca-bundle.pl

@@ -377,6 +377,9 @@ my $newhash= sha256($txt);
 
 if(!$opt_f && $oldhash eq $newhash) {
     report "Downloaded file identical to previous run\'s source file. Exiting";
+    if($opt_u && -e $txt && !unlink($txt)) {
+        report "Failed to remove $txt: $!\n";
+    }
     exit;
 }