Fixing bug #4163. This allows the left thruster to be a missing part …

…correctly.

It does not clear excess missing Thrusters, but they won't return.

MekHQ/src/mekhq/campaign/parts/Thrusters.java

@@ -186,7 +186,7 @@ public void remove(boolean salvage) {
 
     @Override
     public MissingPart getMissingPart() {
-        return new MissingThrusters(getUnitTonnage(), campaign);
+        return new MissingThrusters(getUnitTonnage(), campaign, isLeftThrusters);
     }
 
     @Override