only include stretch tool in stretch histogram

[kecnry]

Description

This pull request removes the stretch bounds tool, introduced in #2513 (milestoned to 3.8, so no need for a bugfix here), from all viewers except the stretch histogram.

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files	Coverage Δ
...nfigs/default/plugins/plot_options/plot_options.py	91.20% <100.00%> (-0.03%)	⬇️
jdaviz/core/template_mixin.py	91.65% <100.00%> (+0.01%)	⬆️

... and 1 file with indirect coverage changes

📢 Thoughts on this report? Let us know!

[rosteen]

I'll admit to still being a little confused about why this was happening in the first place. Were multiple viewers sharing a NestedJupyterToolbar instance?

[kecnry]

I think because it was defined at the class level, other instances initiated later saw the same changes.

[rosteen]

I confirmed that the tool is gone in the viewers for line profiles and aperture photometry. Still don't know how it got there in the first place!