ClientTransaction: don't transport IApplicationThread.

This object is only needed for local in-process calls, and should
never be transported across process boundaries.

This change was made so that we have fewer custom implementations of
IApplicationThread to chase for OWNERS when adding new methods.

Bug: 257972988
Test: TH
Change-Id: I2ab7681cd812ed3ffb9dfb01f6d464fcd0ea81d6