Fix missing backspace key

When hardware keyboard is enabled, the backspace key is missing
and text cannot be delete. This commit handles this special case.

Change-Id: Ifad98797649d54fe566ba122abc2f8c63d8e2820
(cherry picked from commit 4aa2dc79ec8045e300bc3a945ea7f9e13f7c2536)
Merge "Fix missing backspace key" into studio-1.0-dev