Fix issue that Overview key doesn't work at secondary user

If user captures screenshot, screenshot process is started. Screenshot
process also starts services that is defined SERVICES_PER_USER.
As a result Recents class's object is unexpectedly constucted from
screenshot process, and cause to connect with system-user's SystemUI
with mUserToSystemServiceConnection. So, binder proxy from system-user's
SystemUI to secondary-user's SystemUI is replaced with proxy to
screenshot process. In this case Overview key doesn't work at all
until reboot.

Bug:30340532
Change-Id: I84b8b4a02ac3ff781e06d57be19cff56efa76521