Remove translation markers from libpq-be-fe-helpers.h

Apparently these markers cause the modules to not link correctly in some
platforms, at least per buildfarm member indri; moreover, this code is
only used in modules that don't have a translation.  If we someday add
i18n support to contrib/ it might be worth revisiting this.

src/include/libpq/libpq-be-fe-helpers.h

@@ -390,7 +390,7 @@ libpqsrv_cancel(PGconn *conn, TimestampTz endtime)
 
 	cancel_conn = PQcancelCreate(conn);
 	if (cancel_conn == NULL)
-		return _("out of memory");
+		return "out of memory";
 
 	/* In what follows, do not leak any PGcancelConn on any errors. */
 
@@ -418,7 +418,7 @@ libpqsrv_cancel(PGconn *conn, TimestampTz endtime)
 			cur_timeout = TimestampDifferenceMilliseconds(now, endtime);
 			if (cur_timeout <= 0)
 			{
-				error = _("cancel request timed out");
+				error = "cancel request timed out";
 				break;
 			}