Update tls13ccstest.c, removal of deadcode

tst has been already checked for invalid value in the start of the function with switch statement.

Checked again here, so removed deadcode

CLA: trivial

Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #23813)

test/tls13ccstest.c

@@ -471,10 +471,6 @@ static int test_tls13ccs(int tst)
                 || !TEST_size_t_gt(chsessidlen, 0))
             goto err;
         break;
-
-    default:
-        TEST_error("Invalid test value");
-        goto err;
     }
 
     ret = 1;