Remove unused macro

It has never been used.

Author: petere

src/bin/pg_dump/parallel.c

@@ -225,8 +225,6 @@ static char *readMessageFromPipe(int fd);
 
 #define messageStartsWith(msg, prefix) \
 	(strncmp(msg, prefix, strlen(prefix)) == 0)
-#define messageEquals(msg, pattern) \
-	(strcmp(msg, pattern) == 0)
 
 
 /*