gh-35841: deprecate some imports
- Head toward deprecation of automatic imports of some dev tools
- Remove unnecessary assignments in tests/benchmark.py
Deprecate the imports of some dev tools
<!-- Please provide a concise, informative and self-explanatory title.
-->
<!-- Don't put issue numbers in the title. Put it in the Description
below. -->
<!-- For example, instead of "Fixes #12345", use "Add a new method to
multiply two integers" -->
### :books: Description
This is a branch to address #34259, replacing the old trac branch. It
doesn't make all of the original changes: the original branch. In
particular, the original branch added a bunch of lines like `from
sage.misc.misc import cputime` even though the import of `cputime` was
not changes, just in case someone wanted to change it later. I skipped
all of those additions. The original branch made a few other changes
that were not connected to the purposes of this pull request (e.g. the
changes to src/sage/combinat/composition.py), and I skipped those, too.
<!-- Describe your changes here in detail. -->
<!-- Why is this change required? What problem does it solve? -->
<!-- If this PR resolves an open issue, please link to it here. For
example "Fixes #12345". -->
<!-- If your change requires a documentation PR, please link it
appropriately. -->
### :memo: Checklist
<!-- Put an `x` in all the boxes that apply. It should be `[x]` not `[x
]`. -->
- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
- [x] I have updated the documentation accordingly.
### :hourglass: Dependencies
<!-- List all open PRs that this PR logically depends on
- #12345: short description why this is a dependency
- #34567: ...
-->
<!-- If you're unsure about any of these, don't hesitate to ask. We're
here to help! -->
URL: https://github.com/sagemath/sage/pull/35841
Reported by: John H. Palmieri
Reviewer(s): Matthias Köppe
