Stylus gestures features (2/2)

Change-Id: If4fa001a124874b3264ea1980e846e1ab9de50e8
inputmethod: Fixup remove stylus preference for non stylus devices
This commit included following changes

 * Move show stylus icon checkbox to Pointer Settings Category
 * Fixup issues stylus preference doesn't remove if not supported
 * Improve the code remove stylus preference if not supported
 * Remove an unnecessary variable introduced on http://review.cyanogenmod.org/#/c/33774/

Change-Id: Ic83715bab9cd51f5b6e2ad3206b504fb908bebf1