[SRU mantic/linux, jammy/linux, focal/linux, bionic/linux, xenial/linux LP#2055686] drop internal ABI checks

[Andy Whitcroft]

We currently check for ABI changes in the kernel packaging during kernel
builds.  This prevents us building kernels which do not meet ABI
constraints, for example those which unexpectedly drop a module.

This mechanism has some downsides.  Firstly we must maintain the
internal copy of the ABI data from the previous kernel upload to
facilitate delta detection.  Secondly configuration changes can lead to
the loss of a module which is desired but not immediatly obvious leading
to build failures and additional uploads must be performed to recover
wasting developer time.

Our critical requirement is to not sign or release kernels which do not
meet our criteria.  We already validate signing compatibility and
upgradabilty externally gating signing and releasing on those criteria
via the Stable Workflow Manager (SWM).  It makes sense to perform the
ABI checks in the same manner.  SWM has already been modified to use the
produced linux-buildinfo data to perform the equivalent checks and
report those for the kernel via an `abi-testing` task on the associated
tracker.  We therefore propose dropping ABI checks and history data
from the main package trees.

Following this email are patches for all of the current live stable
series.  Proposing for mantic/linux, jammy/linux, focal/linux,
bionic/linux, and xenial/linux.

-apw