TST: Remaining tseries tests reorg (gh14854)
 - [x] closes #14854 
 - [x] tests reorg
 - [x] passes ``git diff upstream/master | flake8 --diff``
 - [x] whatsnew: Moved ```pandas/tseries/tests/*``` to ```pandas/tests/tseries/*```

looks good. can you add a whatsnew note in Other Api changes.