Remove unsed imports from IAccessibilityInputMethodSession.aidl

This is a follow up CL to my previous CL [1], which introduced a new
set of IPC definitions for A11yIME.

When implementing that CL, somehow I left some unused import lines in
IAccessibilityInputMethodSession.aidl.

This CL removes such unnecessary import lines.

This is a mechanical and no-op code clean-up.  There should be no
observable behavior change.

 [1]: I5ff2e804cbcf90828370a0612ff54111130bdff4
      c60176c1

Bug: 215636776
Bug: 234882948
Test: presubmit
Change-Id: Icdf75a31ab5c7697da00e77835f7b8f38835de9c