Remove sanity test in XRecOffIsValid.

Commit 061e7efb changed the rules
for splitting xlog records across pages, but neglected to update this
test.  It's possible that there's some better action here than just
removing the test completely, but this at least appears to get some
of the things that are currently broken (like initdb on MacOS X)
working again.

src/include/access/xlog_internal.h

@@ -154,8 +154,7 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
 
 /* Check if an XLogRecPtr value is in a plausible range */
 #define XRecOffIsValid(xlrp) \
-		((xlrp) % XLOG_BLCKSZ >= SizeOfXLogShortPHD && \
-		 (XLOG_BLCKSZ - (xlrp) % XLOG_BLCKSZ) >= SizeOfXLogRecord)
+		((xlrp) % XLOG_BLCKSZ >= SizeOfXLogShortPHD)
 
 /*
  * The XLog directory and control file (relative to $PGDATA)