Remove redundant "test" prefix from InputMethodAndSubtypeUtilTest

This is a follow up CL to my previous CL [1], which ported multiple
tests from FrameworksCoreTests to RunSettingsLibRoboTests.

The annotation already has @Test so the prefix is not adding new
information.

 [1]: Iad926ffd9806482a5aef0d8c20d2049be40d03c9
      08a3ecea

Bug: 72940586
Test: make RunSettingsLibRoboTests -j
Change-Id: I473a08605ce30fce8898a84be9869a9e176ab292