TST: remove unnecessary assert statements from tests

[bifbof]

In #498 I copied assert locs.as_locations from another test. But we decided in #215 to use locs.as_locations to check validity.
To never copy the old style again, this PR removes all of it from the tests (and in addition I removed some assert True).
As a sidenote, I think some validity checks don`t work, as discussed in #476, but most are fine.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (07b201a) 92.37% compared to head (c972fc0) 92.37%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #499   +/-   ##
=======================================
  Coverage   92.37%   92.37%           
=======================================
  Files          39       39           
  Lines        2019     2019           
  Branches      344      344           
=======================================
  Hits         1865     1865           
  Misses        133      133           
  Partials       21       21           

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[hongyeehh]

Thanks! Merging!