[v0.41 Dep & Rmv] Documentation Audit

[andrijapau]

Context:

This release had some rather large scope deprecations and removals. This PR aims to address any potential fuzz that was accidentally missed in the source code.

Description of the Change:

This PR includes minor adjustments to the deprecation message for,

• gradient_kwargs to the QNode
• Controlled qubit unitary arguments
• MeasurementProcess.return_type (removal in architecture.rst)

Benefits: Cleaner code.

Possible Drawbacks: None identified.

[sc-82824]

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.59%. Comparing base (043be3e) to head (d7bfae3).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7000   +/-   ##
=======================================
  Coverage   99.59%   99.59%           
=======================================
  Files         483      483           
  Lines       46119    46119           
=======================================
  Hits        45934    45934           
  Misses        185      185           

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[JerryChen97]

I made some changes to several local symbols such that src code there less confusing.