Remove redundant OnCheckIsTextEditor()

In [1] we introduced handwriting initiation enhancements which added a
check for View#onCheckIsTextEditor in IMM#checkFocusInternal. This check
is redundant as View#isHandwritingDelegate already ensures that.
Also, having this breaks
testOnCheckIsTextEditorRunOnUIThreadWithInputMethodManagerIsActive which ensures that IMM#isActive() can be called from background thread we should avoid any calls to onCheckIsTextEditor

This CL doesn't have any behavior change

[1]: I0174e15fbbedf88dcd68ebe98333b6b07871985a

Bug: 308827131
Test: atest CtsInputMethodTestCases
Change-Id: Ifa490db69a011aa14eba0328df0a0661f04173ae