Defer UID data removal until after reading is finished

Removing UID data inside readDelta() callbacks causes deadlocks when
BPF data is used. Instead, build a list of UIDs to remove but defer
deletion until after readDelta() returns.

Bug: 177011744
Change-Id: I38e037b89e71b0cb1ba01374189ba8b7af01d632
Signed-off-by: Connor O'Brien <connoro@google.com>