Remove undefined functions from VirtualTouchpadClient.

Fixes a build issue with -O0 due to missing vtable entries.
Removed functions are defined in the base class as pure virtual,
but never defined for the derived class, causing linking to fail.

Test: make NATIVE_COVERAGE=true COVERAGE_PATHS=frameworks
Bug: 116873221
Change-Id: I7ee8a2e478e1137e3b778dfbdca63a2dc3e2a9b1
(cherry picked from commit 29f76abd)