Remove redundant init code from IMMS

As explained in my previous CL [1], InputMethodSettings is guaranteed
to be empty while executing IMMS constructor. Initialization code that
relies on such an empty InputMethodSettings is just redundant and can
be safely removed.

There must be no observable behavior change.

 [1]: Ia2095de2b565a324d3cb55c9054f1352f10cd747

Bug: 305849394
Bug: 347693610
Test: presubmit
Flag: EXEMPT refactor
Change-Id: Ia0892d9348880df0d78d7341e94383e214eb8426