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>