Remove unnecessary (char *) casts [mem]

Remove (char *) casts around memory functions such as memcmp(),
memcpy(), or memset() where the cast is useless.  Since these
functions don't take char * arguments anyway, these casts are at best
complicated casts to (void *), about which see commit 7f798aca1d.

Reviewed-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Discussion: https://www.postgresql.org/message-id/flat/fd1fcedb-3492-4fc8-9e3e-74b97f2db6c7%40eisentraut.org

src/backend/access/transam/xlogreader.c

@@ -794,7 +794,7 @@ restart:
 				readOff = ReadPageInternal(state, targetPagePtr,
 										   pageHeaderSize + len);
 
-			memcpy(buffer, (char *) contdata, len);
+			memcpy(buffer, contdata, len);
 			buffer += len;
 			gotlen += len;