Remove now unnecessary calls to String.intern() in PreferencesService

The preference keys on which String.intern() is called are already
interned when they are put into the EclipsePreferences object since
#33

bundles/org.eclipse.equinox.preferences/src/org/eclipse/core/internal/preferences/PreferencesService.java

@@ -135,10 +135,6 @@ public IStatus applyPreferences(IExportedPreferences preferences) throws CoreExc
 						// preferences that are not in the applied node
 						// will be removed
 						propsToRemove.remove(key);
-						// intern strings we import because some people
-						// in their property change listeners use identity
-						// instead of equals. See bug 20193 and 20534.
-						key = key.intern();
 						String value = node.get(key, null);
 						if (value != null) {
 							if (EclipsePreferences.DEBUG_PREFERENCE_SET) {
@@ -150,7 +146,6 @@ public IStatus applyPreferences(IExportedPreferences preferences) throws CoreExc
 					}
 				}
 				for (String keyToRemove : propsToRemove) {
-					keyToRemove = keyToRemove.intern();
 					if (EclipsePreferences.DEBUG_PREFERENCE_SET) {
 						PrefsMessages.message("Removing: " + globalNode.absolutePath() + '/' + keyToRemove); //$NON-NLS-1$
 					}