debian: remove -dbg packages from the control file

debian: remove -dbg packages from the control file

It looks like Debian's upload automation will reject a control file
that has packages that it doesn't recognize, even if they are not
built in the default build profile.  (e.g., the expectation is that
build profiles will *disable* packages, but not *add* new binary
packages not normally built.)

So move the offending lines into debian/control.legacy-dbg which is
tacked onto the debian/control file via "./debian/rules debian-files"
and then removed via "./debian/rules mrproper".  It's a hack, but it's
only needed when building backports for Debian Jessie.

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