Drop support for Debian <= 7

[credbbl]

Description

Debian 7 "Wheezy" is EOL since 2018. Just drop support for it completely.

PR information

• The title of the PR is clear and informative.
• There are a small number of commits, each of which has an informative message. This means that previously merged commits do not appear in the history of the PR. For information on cleaning up the commits in your pull request, see this page.
• If applicable, the PR references the bug/issue that it fixes in the description.
• New Unit tests were added for the changes made

Quality of Code and Contribution Guidelines

• I have read the contribution guidelines.

[codecov]

Codecov Report

Merging #2660 (33bdb69) into develop (3aebcdd) will decrease coverage by 0.02%.
The diff coverage is 81.81%.

❗ Current head 33bdb69 differs from pull request most recent head d3aafdb. Consider uploading reports for the commit d3aafdb to get more accurate results

@@             Coverage Diff             @@
##           develop    #2660      +/-   ##
===========================================
- Coverage    71.97%   71.95%   -0.03%     
===========================================
  Files          103      103              
  Lines        15692    15669      -23     
  Branches      2486     2484       -2     
===========================================
- Hits         11295    11274      -21     
+ Misses        3881     3879       -2     
  Partials       516      516              

Impacted Files	Coverage Δ
azurelinuxagent/common/osutil/debian.py	70.83% <75.00%> (-9.17%)	⬇️
azurelinuxagent/common/osutil/factory.py	92.94% <100.00%> (-0.17%)	⬇️

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[narrieta]

@credbbl We are still receiving telemetry from Debian 7 VMs so we will leave this code as is for the moment.