Revert tab key behavior on multiline EditTexts.

This CL reverts ag/10267783 effectively.
ag/10267783 makes tab key insert \t character on multiline text fields,
however, it broke the existing apps which depends on the previous
behavior.

Bug: 154290658
Test: manual - Tab key on multiline text fields advance focus
Test: atest TextViewTest#testKeyNavigation
Change-Id: I9836ce29321ca789bce6636514ce9a8dbf923ada