adt-installer: Drop since its replaced by the extensible SDK

The extensible SDK replaces adt-installer so this can be removed now,
all future effort in this direction will be placed onto that.

This includes a layer version change so the autobuilder knows when to
stop building adt-installer.

[YOCTO #6404]

(From OE-Core rev: c413164c03bdce38f41e63ad2a27dc6108521b9a)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>