Remove requestCursorUpdatesFromImm() again

This CL removes an unused method

  RemoteInputConnectionImpl#requestCursorUpdatesFromImm(),

which was originally introduced [1] then removed [2], and
accidentally added again [3].

Anyway, this method is no longer used and can be removed safely.

 [1]: I3d6b1728d62139785593af14c24cb52bf2c91e31
      71aa1a31
 [2]: Ia72a9fe0ceac1798ee1989eaae3906e8e1b696bf
      5854c92b
 [3]: I53bcb62e03ac1c371feb60d1385c88c921754092
      3e3ff1a3

Bug: 210039666
Test: presubmit
Change-Id: I4d0bf0ac371e1f9f214258906231d6ae85bdce3e