SF: Update the cached display modes in HWComposer on hotplug

Currently configs in HWComposer are cached only once
per display and never updated on subseqent onHotplug
events. This may cause setActiveConfigsWithConstraints
to fail for a valid config.

This CL also removes the test HandleTransactionLockedTest::
processesHotplugConnectPrimaryDisplayWithExternalAlreadyConnected,
since it's testing an unsupported use case and its
incompatible with the tests we've added.

Bug: 159590486
Test: atest HWComposerConfigsTest
Change-Id: Ifb22c33ba5078bde35ae20a2f94a8630316da024