Frontend GUI: Remove default of Enter as Long Press

Keys assigned as Long Press may not work with lirc, so Enter may stop
working for some users. Remove the default that caused this.
Users will have to manually add keys they want to use with Long Press.

Refs #13234

mythtv/libs/libmythui/mythmainwindow.cpp

@@ -1393,7 +1393,7 @@ void MythMainWindow::InitKeys()
     RegisterKey("Main Menu",    "STANDBYMODE",QT_TRANSLATE_NOOP("MythControls",
         "Enter Standby Mode"),              "");
     RegisterKey("Long Press",    "LONGPRESS1",QT_TRANSLATE_NOOP("MythControls",
-        "Up to 16 Keys that allow Long Press"),      "Enter");
+        "Up to 16 Keys that allow Long Press"),      "");
     RegisterKey("Long Press",    "LONGPRESS2",QT_TRANSLATE_NOOP("MythControls",
         "Up to 16 Keys that allow Long Press"),      "");
     RegisterKey("Long Press",    "LONGPRESS3",QT_TRANSLATE_NOOP("MythControls",