gr_filter : Remove adaptive filter code.

This code has several coverity issues. Looking at the code showed no
in tree users, even in the in tree adaptive filters. Rather than try and
fix the issues here, or make the adaptive filters use this code. I
chose to remove the code. I also googled some and couldn't find public
users.

Resolves CID 1043256, 1046173 and 1046409.

Signed-off-by: Philip Balister <philip@balister.org>
digital: HPD fixes (burst ID tags are no more propagated; buffer sizes are halved to est. max output size)
modtool: bugfixes for in-tree operation (include paths, license, cmake editing)
blocks: fix pdu_to_tagged_stream when saving leftover items
Merge branch 'maint'
Merge remote-tracking branch 'balister/adap'
Merge remote-tracking branch 'martin/hpd-modtool-fixes' into maint
Merge branch 'maint'