Remove superfluous newlines in function prototypes.

These were introduced by pgindent due to fixe to broken
indentation (c.f. 8255c7a5ee). Previously the mis-indentation of
function prototypes was creatively used to reduce indentation in a few
places.

As that formatting only exists in master and REL_12_STABLE, it seems
better to fix it in both, rather than having some odd indentation in
v12 that somebody might copy for future patches or such.

Author: Andres Freund
Discussion: https://postgr.es/m/20190728013754.jwcbe5nfyt3533vx@alap3.anarazel.de
Backpatch: 12-

src/include/replication/reorderbuffer.h

@@ -292,34 +292,29 @@ typedef struct ReorderBufferTXN
 typedef struct ReorderBuffer ReorderBuffer;
 
 /* change callback signature */
-typedef void (*ReorderBufferApplyChangeCB) (
-											ReorderBuffer *rb,
+typedef void (*ReorderBufferApplyChangeCB) (ReorderBuffer *rb,
 											ReorderBufferTXN *txn,
 											Relation relation,
 											ReorderBufferChange *change);
 
 /* truncate callback signature */
-typedef void (*ReorderBufferApplyTruncateCB) (
-											  ReorderBuffer *rb,
+typedef void (*ReorderBufferApplyTruncateCB) (ReorderBuffer *rb,
 											  ReorderBufferTXN *txn,
 											  int nrelations,
 											  Relation relations[],
 											  ReorderBufferChange *change);
 
 /* begin callback signature */
-typedef void (*ReorderBufferBeginCB) (
-									  ReorderBuffer *rb,
+typedef void (*ReorderBufferBeginCB) (ReorderBuffer *rb,
 									  ReorderBufferTXN *txn);
 
 /* commit callback signature */
-typedef void (*ReorderBufferCommitCB) (
-									   ReorderBuffer *rb,
+typedef void (*ReorderBufferCommitCB) (ReorderBuffer *rb,
 									   ReorderBufferTXN *txn,
 									   XLogRecPtr commit_lsn);
 
 /* message callback signature */
-typedef void (*ReorderBufferMessageCB) (
-										ReorderBuffer *rb,
+typedef void (*ReorderBufferMessageCB) (ReorderBuffer *rb,
 										ReorderBufferTXN *txn,
 										XLogRecPtr message_lsn,
 										bool transactional,