Remove sqlite3_selfsigned.sis as it is no longer usable or needed.

Remove sqlite3_selfsigned.sis as it is no longer usable or needed.

Selfsigned qt.sis no longer installs on top of sqlite3_selfsigned.sis
as patching embedded sises and dependencies was removed from
patch_capabilities.pl script. However, since the regular sqlite3.sis
is nowadays signed for all three Symbian manufacturers that Qt supports,
there is no more need to have a self-signed sqlite3.sis in the first
place, so it is removed to reduce confusion.

Task-number: QTBUG-16576
Reviewed-by: axis
(cherry picked from commit 99f500838e4eaba9d99c3ea2cd6b4fc5efe0b8b4)