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/xlog.c

@@ -2089,7 +2089,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, TimeLineID tli, bool opportunistic)
 		 * Be sure to re-zero the buffer so that bytes beyond what we've
 		 * written will look like zeroes and not valid XLOG records...
 		 */
-		MemSet((char *) NewPage, 0, XLOG_BLCKSZ);
+		MemSet(NewPage, 0, XLOG_BLCKSZ);
 
 		/*
 		 * Fill the new page's header

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;