refactor: remove SwarmMode/DockerCE orchestrator

[mboersma]

Reason for Change:
Removes code supporting the SwarmMode/DockerCE orchestrator, as a first step toward removing all old orchestrator code in AKS Engine.

Issue Fixed:
Refs #2500

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:
This is still a size/XXL PR. Does it seem reviewable? Others may be of a similar size.

[mboersma]

/hold

This is premature: I'm still waiting for feedback on #2500, we should wait until closer to the ACS end-of-life date, and it's the holiday season. 🎄

[acs-bot]

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[codecov]

Codecov Report

Merging #2502 into master will decrease coverage by 0.13%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2502      +/-   ##
==========================================
- Coverage    72.7%   72.57%   -0.14%     
==========================================
  Files         130      130              
  Lines       24105    24022      -83     
==========================================
- Hits        17526    17433      -93     
- Misses       5553     5566      +13     
+ Partials     1026     1023       -3

[mboersma]

The word on the street is that ACS may receive a stay of execution, so the old orchestrator code may need to be preserved (if not updated...).