Simplify the Key's on state transition

Because handling shift locked state of alphabet keyboard is done by
KeyboardSwitcher, there is no need to change the "on" state of Key
when releasing the key. On the other hand, symbol and symbol shifted
keyboard has fixed "on" state "ALT/MORE" key.

This change also renames the attribute "isModifier" to "isFunctional".

Change-Id: I082885bd2376ae26bdfc378c14add2b5d6be1d4e
diff --git a/java/res/values/attrs.xml b/java/res/values/attrs.xml
index f0da274..28c948b 100644
--- a/java/res/values/attrs.xml
+++ b/java/res/values/attrs.xml
@@ -107,8 +107,8 @@
             <!-- Key is anchored to the right of the keyboard. -->
             <flag name="right" value="2" />
         </attr>
-        <!-- Whether this is a modifier key such as Alt or Shift. -->
-        <attr name="isModifier" format="boolean" />
+        <!-- Whether this is a functional key which has different key top than normal key. -->
+        <attr name="isFunctional" format="boolean" />
         <!-- Whether this is a toggle key. -->
         <attr name="isSticky" format="boolean" />
         <!-- Whether long-pressing on this key will make it repeat. -->