Get rid of the Debian package manager.

[pattivacek]

It never really worked and was only used in two places:

1. A memory usage test that isn't very useful anymore. It's been removed.
2. As part of the Debian packaging, which didn't really make sense. It's been replaced with the regular sota-local.toml.

[codecov-commenter]

Codecov Report

Merging #1739 into master will increase coverage by 1.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1739      +/-   ##
==========================================
+ Coverage   72.49%   73.58%   +1.08%     
==========================================
  Files         180      178       -2     
  Lines       14121    13884     -237     
==========================================
- Hits        10237    10216      -21     
+ Misses       3884     3668     -216     

Impacted Files	Coverage Δ
include/libaktualizr/config.h	100.00% <ø> (ø)
include/libaktualizr/packagemanagerinterface.h	60.00% <0.00%> (-20.00%)	⬇️
src/libaktualizr/config/config.cc	65.75% <0.00%> (-0.78%)	⬇️
src/libaktualizr/package_manager/ostreemanager.cc	51.50% <0.00%> (+0.23%)	⬆️
src/libaktualizr/utilities/utils.cc	54.83% <0.00%> (+0.62%)	⬆️
src/libaktualizr/crypto/crypto.cc	84.76% <0.00%> (+0.66%)	⬆️
src/aktualizr_info/main.cc	94.04% <0.00%> (+0.85%)	⬆️
src/libaktualizr/primary/sotauptaneclient.h	60.71% <0.00%> (+3.08%)	⬆️
src/libaktualizr/storage/sqlstorage_base.cc	79.59% <0.00%> (+4.76%)	⬆️
...tualizr/package_manager/packagemanagerinterface.cc	65.67% <0.00%> (+5.60%)	⬆️
... and 7 more

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