Say only what a tail coupler does: end signals or none

The simulator reads the last vehicle's coupler for one thing, whether to put
up the end signals. It does not couple the train to anything behind it, as
the tooltip and a comment claimed.

StarterNG/startercfg/lang/en.xml

@@ -290,7 +290,7 @@
     <String key="CouplerFree">The vehicles are not coupled.</String>
     <String key="CouplerConnects">Connected: {0}</String>
     <String key="CouplerEndSignals">End of the train — the simulator puts up the end signals.</String>
-    <String key="CouplerCoupledBehind">The end of the train couples to whatever stands behind it ({0}) — no end signals.</String>
+    <String key="CouplerNoEndSignals">Anything but 0 at the back of the train — the simulator puts up no end signals.</String>
     <String key="CouplerLocked">Locked — not uncoupled in shunting.</String>
     <String key="CouplerClickToEdit">Click to change.</String>
     <String key="AddVehicle">Add</String>