Stop watching for system property changes when all view is removed.

Bug: none
Flag: EXEMPT minor optimization
(cherry picked from https://android-review.googlesource.com/q/commit:69bad058fd2d205c2595a017262839fa36ab3f63)
Merged-In: I2761cb9e6126240386c2dc24e8886d59b6fa0891
Change-Id: Ibc3d77da38f29a072e35c9301569026524b141e3