SystemUI: unregister ContentObserver

We were leaking memory.

PS2: move instanciating to the SearchPanelView constructor
PS3: more possible memory leaks

Change-Id: Ie9ddf00c698692f418cb8ef473dff2b1aa05135d
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>
Signed-off-by: PipelinerArd <kristoferard@gmail.com>

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/policy/SignalText.java