libpdx: Remove superfluous DispatchRemoteMethod overloads.

The introduction of RemoteMethodReturn<>() properly handles the
differences between most of these overloads. Remove the ones that
are now obsolete in favor of the generic version.

Bug: None
Test: make -j30
Change-Id: I23e63431e9f668c324b408707ce65e7d6aee69c8