Move followedBy/forEffect tests to ApplyTests

[peterneyens]

Move the followedBy and forEffect consistency tests from FlatMapTests to ApplyTests.

Small follow up on #1955.

[johnynek]

👍

[codecov-io]

Codecov Report

Merging #1963 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1963   +/-   ##
=======================================
  Coverage   96.07%   96.07%           
=======================================
  Files         273      273           
  Lines        4538     4538           
  Branches      117      122    +5     
=======================================
  Hits         4360     4360           
  Misses        178      178

Impacted Files	Coverage Δ
...main/scala/cats/laws/discipline/FlatMapTests.scala	100% <ø> (ø)	⬆️
...c/main/scala/cats/laws/discipline/ApplyTests.scala	100% <100%> (ø)	⬆️

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