Remove duplicate separator definition.

INPUT_METHOD_SEPARATOR and INPUT_METHOD_SUBTYPE_SEPARATOR are defined in
both InputMethodUtils and InputMethodSettings with same value.
This CL removes definitions in InputMethodSettings and use SEPARATOR
instead of SEPARATER.

INPUT_METHOD_SEPARATOR and INPUT_METHOD_SUBTYPE_SEPARATOR in
InputMethodUtils are originally introduced to IMMS by
If0104151b3526da6ecc669adde3119a239ecafeb and they are moved to
InputMethodUtils by I01f5fafbbcfe3e3f5313829162ec011eaf2ad991.

INPUT_METHOD_SEPARATER and INPUT_METHOD_SUBTYPE_SEPARATER in
InputMethodSettings are originally introducced to IMMS as a part of
IMMS.InputMethodSettings by Icd0f13de396ce286ff6563e8c2775d53bcdacbf3
and InputMethodSettings is moved to InputMethodSettings by
I0bc9954f163a3ec38d08b9ba842a8a31176eb6a6

Bug: 22285167
Change-Id: I3601c10902b44bb639581e3b816a3fc0a4851957