Remove ShellInit/ShellCommandHandler interfaces to SysUI

- SysUI now calls init/commands/dump via the ShellController interface
- Move ShellInit/ShellCommandHandler into the sysui package since it's
  only called on sysui startup

Test: atest WMShellUnitTests
Test: atest SystemUITests
Bug: 238217847
Change-Id: I7b05dbab7648cb8a8c6f9381b0b5f545ed3398f1