Remove unused methods from InputMethodUtilsTest

This is a follow up CL to my previous CL [1], which removed

  InputMethodUtilsTest#testInputMethodSettings_SwitchCurrentUser()

but forgot to remove

  TestContext.getSecondaryUserContext().

 [1]: I52297912d0b66e5e40b6a624c35427a377dc7b1b
      a56463ba

Bug: 309837937
Bug: 309868254
Test: atest InputMethodUtilsTest
Change-Id: I8f39bc96caa14e7c4e9a5b3f71c95a6211597b4a