Fix RollbackTest#testBadUpdateRollback

It appears that the device can be under high broadcast pressure and 5
seconds may not be a long enough wait to receive broadcast from test
app in instrumented app. We now remove the 5 seconds wait and rely on
test runner timeout to not wait forever.

Test: atest RollbackTest
Bug: 123886893 120598832
Change-Id: Ic686da15cfb64e5a84fb9f7c2795b94ef481d3bd