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: atest DeviceBootTest
Change-Id: I23f186db97902ad4f7f7b3e53b7282e3a1200251