Removed call to tail, and the 'watchPulser' test

[TimSheard]

The following test causes a failure on Master

TASTY_PATTERN='/Watch pulser on traces of length 120./' cabal test --test-options "--quickcheck-replay=433821"

to make a step test, where we test a property on every (state{n}, state{n+1}) pair in trace we used the following pattern
pairs = zip states (tail states)
But in very rare occasions, when the number of states is 0 or 1, tail raises the empty List error.
We can easily fix this by pattern matching, and return true when that is the case.

We also removed the '/Watch pulser on traces of length 120./' test, which uses trace and prints too much stuff.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated. If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages. New section is never added with the code changes. (See RELEASING.md)
• Code is formatted with fourmolu (use scripts/fourmolize.sh)
• Cabal files are formatted (use scripts/cabal-format.sh)
• hie.yaml has been updated (use scripts/gen-hie.sh)
• Self-reviewed the diff

[lehins]

Just a little linting. Otherwise its great.