Do not start SelectionToolbarManagerService for Wear

The logic to get the SelectionToolbarManager API class has also been
updated to ensure that no call to Context.getSystemService made for
SelectionToolbarManager does not cause crashes.

Bug: 407778313
Flag: EXEMPT minor change, removing service not used on Wear
Test: presubmit, and tests (see CL topic)
Change-Id: Ice836d1ca3908ffe284fd98c886e4bcf89560614