Remove clear/restore callingUid

We no longer need to do this because UserManager.getUserHandles and
PackageManager.getInstalledPackagesAsUser are now called in a separate
background thread.

Bug: 130773130
Test: adb shell stop statsd && adb shell start statsd. Manually verified
that the uidmap was sent successfully.

Change-Id: Ifde1ba09575a479952bdbcd98aec4c34b3210974