Do not spell check the foreground ExtractEditText.

Bug 5755099

In extracted text mode, we spell check the background and the foreground
edit text. All changes in the background are already propagated to the
foreground, and updates on the foreground may trigger a spell check
of the entire text since we use setText.

Change-Id: Ie44c3d9113258082ac6df5890851d0e21c702ea2