Delete the old implementation of PeopleSpaceActivity

This CL deletes the old code of the PeopleSpaceActivity. The new Compose
implementation has been enabled since September in ag/24789231.

Bug: 293570761
Test: N/A. Pure code deletion.
Flag: EXEMPT deletes unused code turned off by legacy flag.
Change-Id: I1feac430788714274f63acf2bddb3ba987e2f67d