debian: convert to use build profile rules exclusively

debian: convert to use build profile rules exclusively

This commit drops support for the debian/rules.custom file, and only
relies on build profiles.

This means we no longer need to build the control file from
control.in, which simplifies this; developers can now build a debian
package immediately after checking out the tree from git.  This also
implies that we are dropping support for Debian 7 (wheezy) and Ubuntu
Trusty (14.04LTS) and older releases.  (People who want to backport to
these older distributions will have to make manual adjustments to the
debian/control and debian/rules files.)

Instead of using SKIP_E2FSCK_STATIC in debian/rules.custom, use the
new build profile: pkg.e2fsprogs.no-static-e2fsck

Support for the old-style *-dbg files used in Debian Jessie (which did
not support dbgsym packages) is completely automated.  The system will
auto-detect systems which do not support dbgsym and automatically set
the pkg.e2fsprogs.legacy-pkg build profile.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>