Tidy up of unused imports

[GarethCabournDavies]

Remove unused imports from codes throughout the repository
This should save time during the running of the codes, as well as helping move towards a code-checked-before-merging model.

Standard information about the request

This change should have absolutely no effect, but changes are in every part of the code base

This change: follows style guidelines (See e.g. PEP8), has been proposed using the contribution guidelines

Motivation

Want to start improving quality and checking whether submitted code meets quality requirements

Contents

Used flake8 to find unused imports, if there were any, then get rid of them
The files chosen were:

• anything under bin which started with pycbc_
• anything under pycbc which ends .py, but ignore any __init__.py or the special version.py
• anything under test which ends .py - ignore the scheme testing as that uses try/except-wrapped imports, which fail flake8

Links to any issues or associated PRs

Issue raised in #4999

• The author of this pull request confirms they will adhere to the code of conduct

[titodalcanton]

Can the new action effectively replace the old Code Climate checks?

[GarethCabournDavies]

Can the new action effectively replace the old Code Climate checks?

At the moment, it is looking for unused imports only (the select=F401 flag), but it may be able to replace these eventually. It hasn't actually picked up the action though, so I will try to work out why

[spxiwh]

To comment on codeclimate ... It is easy to run the tools that it uses ... They are all open source standard tools etc. It is not so easy to parse the results, figure out what complaints (there will be many complaints) are new and what are pre-existing, and present this to the user (with a pass/fail). Doing all this in a GUI is the value that CodeClimate (or the older thing, who's name I forgot) adds, and is the bit that is not open source.

[spxiwh]

TL:DR