SystemUI: unregister ContentObserver

We were leaking memory.

PS2: move instanciating to the SearchPanelView constructor

Change-Id: Ie9ddf00c698692f418cb8ef473dff2b1aa05135d
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>
Merge commit 'refs/changes/10/6810/2' of http://gerrit.sudoservers.com/AOKP/frameworks_base into jb-mr1