stop publishing cats all bundle , start to publish cats-testkit

[kailuowang]

fixes #1682

[codecov-io]

Codecov Report

Merging #1758 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1758      +/-   ##
==========================================
- Coverage   94.17%   94.13%   -0.05%     
==========================================
  Files         256      259       +3     
  Lines        4208     4247      +39     
  Branches       93       98       +5     
==========================================
+ Hits         3963     3998      +35     
- Misses        245      249       +4

Impacted Files	Coverage Δ
...stkit/src/main/scala/cats/tests/CatsEquality.scala	66.66% <ø> (ø)
testkit/src/main/scala/cats/tests/Helpers.scala	100% <ø> (ø)
testkit/src/main/scala/cats/tests/CatsSuite.scala	80% <ø> (ø)
core/src/main/scala/cats/Show.scala	100% <0%> (ø)	⬆️

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[andyscott]

Looks good. I tested publishLocal and all the artifacts were generated as expected.

[edmundnoble]

Merging with two (plus two) approvals.