repmgr: fix generation of default "dbname"

If not explicitly provided, "dbname" was being set early to the default
"username" value, which was leading to different behaviour to libpq
applications, where "dbname" defaults to "username" at connection
time.

repmgr.c

@@ -283,7 +283,11 @@ main(int argc, char **argv)
 
 	/*
 	 * Pre-set any defaults , which can be overwritten if matching
-	 * command line parameters are provided
+	 * command line parameters are provided.
+	 *
+	 * Note: PQconndefaults() does not provide a default value for
+	 * "dbname", but if none is provided will default to "username"
+	 * when the connection is made.
 	 */
 
 	for (c = 0; c < source_conninfo.size && source_conninfo.keywords[c]; c++)
@@ -316,7 +320,6 @@ main(int argc, char **argv)
 	}
 
 	/* set default user for -R/--remote-user */
-
 	{
 		struct passwd *pw = NULL;
 
@@ -330,15 +333,6 @@ main(int argc, char **argv)
 		strncpy(runtime_options.username, pw->pw_name, MAXLEN);
 	}
 
-	/*
-	 * Though libpq will default to the username as dbname, PQconndefaults()
-	 * doesn't return this
-	 */
-	if (runtime_options.dbname[0] == '\0')
-	{
-		strncpy(runtime_options.dbname, runtime_options.username, MAXLEN);
-	}
-
 	while ((c = getopt_long(argc, argv, "?Vd:h:p:U:S:D:f:R:w:k:FWIvb:rcL:tm:C:l:P", long_options,
 							&optindex)) != -1)
 	{