Removes support for old protocols in Copy functions from PG14

Some Copy related functions copied from Postgres had support for both old and new protocols
Postgres removed support for old version so we remove it too

Relevant PG commit:
3174d69fb96a66173224e60ec7053b988d5ed4d9

src/backend/distributed/commands/multi_copy.c

@@ -67,6 +67,7 @@
 #include "catalog/pg_type.h"
 #include "commands/copy.h"
 #include "commands/defrem.h"
+#include "commands/progress.h"
 #include "distributed/citus_safe_lib.h"
 #include "distributed/commands/multi_copy.h"
 #include "distributed/commands/utility_hook.h"
@@ -1806,24 +1807,8 @@ CreateEmptyShard(char *relationName)
 static void
 SendCopyBegin(CopyOutState cstate)
 {
-	if (PG_PROTOCOL_MAJOR(FrontendProtocol) >= 3)
-	{
-		/* new way */
-		StringInfoData buf;
-		int			natts = list_length(cstate->attnumlist);
-		int16		format = (cstate->binary ? 1 : 0);
-		int			i;
-
-		pq_beginmessage(&buf, 'H');
-		pq_sendbyte(&buf, format);	/* overall format */
-		pq_sendint16(&buf, natts);
-		for (i = 0; i < natts; i++)
-			pq_sendint16(&buf, format); /* per-column formats */
-		pq_endmessage(&buf);
-		cstate->copy_dest = COPY_NEW_FE;
-	}
-	else
-	{
+#if PG_VERSION_NUM < PG_VERSION_14
+	if (PG_PROTOCOL_MAJOR(FrontendProtocol) < 3) {
 		/* old way */
 		if (cstate->binary)
 			ereport(ERROR,
@@ -1833,7 +1818,21 @@ SendCopyBegin(CopyOutState cstate)
 		/* grottiness needed for old COPY OUT protocol */
 		pq_startcopyout();
 		cstate->copy_dest = COPY_OLD_FE;
+		return;
 	}
+#endif
+	StringInfoData buf;
+	int			natts = list_length(cstate->attnumlist);
+	int16		format = (cstate->binary ? 1 : 0);
+	int			i;
+
+	pq_beginmessage(&buf, 'H');
+	pq_sendbyte(&buf, format);	/* overall format */
+	pq_sendint16(&buf, natts);
+	for (i = 0; i < natts; i++)
+		pq_sendint16(&buf, format); /* per-column formats */
+	pq_endmessage(&buf);
+	cstate->copy_dest = COPY_FRONTEND;
 }
 
 
@@ -1841,20 +1840,20 @@ SendCopyBegin(CopyOutState cstate)
 static void
 SendCopyEnd(CopyOutState cstate)
 {
-	if (cstate->copy_dest == COPY_NEW_FE)
-	{
-		/* Shouldn't have any unsent data */
-		Assert(cstate->fe_msgbuf->len == 0);
-		/* Send Copy Done message */
-		pq_putemptymessage('c');
-	}
-	else
+#if PG_VERSION_NUM < PG_VERSION_14
+	if (cstate->copy_dest != COPY_NEW_FE)
 	{
 		CopySendData(cstate, "\\.", 2);
 		/* Need to flush out the trailer (this also appends a newline) */
 		CopySendEndOfRow(cstate, true);
 		pq_endcopyout(false);
+		return;
 	}
+#endif
+	/* Shouldn't have any unsent data */
+	Assert(cstate->fe_msgbuf->len == 0);
+	/* Send Copy Done message */
+	pq_putemptymessage('c');
 }
 
 
@@ -1908,6 +1907,7 @@ CopySendEndOfRow(CopyOutState cstate, bool includeEndOfLine)
 
 	switch (cstate->copy_dest)
 	{
+#if PG_VERSION_NUM < PG_VERSION_14
 		case COPY_OLD_FE:
 			/* The FE/BE protocol uses \n as newline for all platforms */
 			if (!cstate->binary && includeEndOfLine)
@@ -1921,7 +1921,8 @@ CopySendEndOfRow(CopyOutState cstate, bool includeEndOfLine)
 						 errmsg("connection lost during COPY to stdout")));
 			}
 			break;
-		case COPY_NEW_FE:
+#endif
+		case COPY_FRONTEND:
 			/* The FE/BE protocol uses \n as newline for all platforms */
 			if (!cstate->binary && includeEndOfLine)
 				CopySendChar(cstate, '\n');

src/include/distributed/commands/multi_copy.h

@@ -31,8 +31,12 @@
 typedef enum CitusCopyDest
 {
 	COPY_FILE,                  /* to/from file (or a piped program) */
+#if PG_VERSION_NUM >= PG_VERSION_14
+	COPY_FRONTEND,              /* to frontend */
+#else
 	COPY_OLD_FE,                /* to/from frontend (2.0 protocol) */
 	COPY_NEW_FE,                /* to/from frontend (3.0 protocol) */
+#endif
 	COPY_CALLBACK               /* to/from callback function */
 } CitusCopyDest;
 

src/include/distributed/version_compat.h

@@ -54,6 +54,7 @@
 	standard_ProcessUtility(a, b, c, d, e, f, g, h)
 #define ProcessUtility_compat(a, b, c, d, e, f, g, h) \
 	ProcessUtility(a, b, c, d, e, f, g, h)
+#define COPY_FRONTEND_COMPAT COPY_FRONTEND
 #else
 #define AlterTableStmtObjType(a) ((a)->relkind)
 #define F_NEXTVAL_COMPAT F_NEXTVAL_OID
@@ -80,6 +81,7 @@
 #define standard_ProcessUtility_compat(a, b, c, d, e, f, g, h) \
 	standard_ProcessUtility(a, b, d, e, f, g, h)
 #define ProcessUtility_compat(a, b, c, d, e, f, g, h) ProcessUtility(a, b, d, e, f, g, h)
+#define COPY_FRONTEND_COMPAT COPY_NEW_FE
 #endif
 
 #if PG_VERSION_NUM >= PG_VERSION_13