Fix test-cp-name-parser build, unused variable

$ make test-cp-name-parser
  ...
  CXX    test-cp-name-parser.o
  src/gdb/cp-name-parser.y: In function ‘int gdb::main(int, char**)’:
  src/gdb/cp-name-parser.y:2137:6: error: unused variable ‘len’ [-Werror=unused-variable]
    int len;
	^~~
  cc1plus: all warnings being treated as errors

gdb/ChangeLog:
2019-03-12  Pedro Alves  <palves@redhat.com>

	* cp-name-parser.y (main): Remove unused 'len' variable.

gdb/ChangeLog

@@ -1,3 +1,7 @@
+2019-03-12  Pedro Alves  <palves@redhat.com>
+
+	* cp-name-parser.y (main): Remove unused 'len' variable.
+
 2019-03-12  Tom Tromey  <tromey@adacore.com>
 
 	* common/ptid.c (null_ptid, minus_one_ptid): Now const.

gdb/cp-name-parser.y

@@ -2129,7 +2129,6 @@ main (int argc, char **argv)
   if (argv[arg] == NULL)
     while (fgets (buf, 65536, stdin) != NULL)
       {
-	int len;
 	buf[strlen (buf) - 1] = 0;
 	/* Use DMGL_VERBOSE to get expanded standard substitutions.  */
 	c = trim_chars (buf, &extra_chars);