Remove dead code.

Commit 13629df5 changed metaphone() function to return an empty string on
empty input, but it left the old error message in place. It's now dead code.

Michael Paquier, per Coverity warning.

contrib/fuzzystrmatch/fuzzystrmatch.c

@@ -280,11 +280,6 @@ metaphone(PG_FUNCTION_ARGS)
 				 errmsg("argument exceeds the maximum length of %d bytes",
 						MAX_METAPHONE_STRLEN)));
 
-	if (!(str_i_len > 0))
-		ereport(ERROR,
-				(errcode(ERRCODE_ZERO_LENGTH_CHARACTER_STRING),
-				 errmsg("argument is empty string")));
-
 	reqlen = PG_GETARG_INT32(1);
 	if (reqlen > MAX_METAPHONE_STRLEN)
 		ereport(ERROR,