RF: remove travis CI setup + badge from README.md

[yarikoptic]

We are using paid travis CI, and funds for that line are about to end. Moreover @mih is also paying for appveyor. So I think it would be reasonable to remove travis. The tricky part would be to get coverage parity since travis has AFAIK more extended battery of matrix runs to excercise different deployment scenarios ATM.

TODOs

• see what we can do to increase coverage back to some only minimal difference

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.28% ⚠️

Comparison is base (776f465) 91.51% compared to head (1570eb1) 91.24%.

Additional details and impacted files

@@            Coverage Diff             @@
##            maint    #7492      +/-   ##
==========================================
- Coverage   91.51%   91.24%   -0.28%     
==========================================
  Files         325      325              
  Lines       43443    43429      -14     
  Branches     5827     5827              
==========================================
- Hits        39759    39625     -134     
- Misses       3669     3789     +120     
  Partials       15       15              

see 42 files with indirect coverage changes

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[mih]

I support this move.

Given the runtime of the test battery, I suspect that the goal of reaching coverage parity is something that will require a long time.

[adswa]

I support this, too. Do I see correctly that the coverage loss is already minimal (-0.28%)? From a cursory read, I guess we mostly loose the breadth of versions, e.g. Python 3.11 or minimal git-annex version

[yarikoptic]

Loss in code % is indeed small, but as you can assess - it would loose coverage of "interesting usecases" (more logging, specific git-annex setups, etc). I would really like to combine some of those and add at least 1 or 2 matrix runs to .appveyor to mimic at least some of those so we do not completely loose testing those code paths.