libaudiohal@aidl: Remove non-working code for HAL PIDs retrieval

Since native audio_server does not have "list services" permission,
it is always being denied to get services debug info (which includes
PIDs). Effectively, `DevicesFactoryHalAidl::getHalPids` never works.
The job of retrieval of HAL PIDs is actually done by the Java
AudioService. The code in libaudiohal@aidl triggers an SELinux
denial and thus should be removed.

Bug: 314853580
Test: check kernel log for 'avc:  denied  { list }'
Test: DeviceBootTest
(cherry picked from commit db666111)
Change-Id: I5fb8e0a98a49141ec488e4faa04274eba46f80fa