Remove QubitStateVector class

[andrijapau]

Context:

Completing the deprecation cycle of QubitStateVector.

Description of the Change:

1. Update deprecations.rst
2. Update changelog-dev.md
3. Remove all deprecated source code

Also, updated CI to install latest pennylane-qiskit rather than stable.

References found in,

• Catalyst: Delete references to the removed QubitStateVector class catalyst#1289
• Lightning: Delete references to the removed QubitStateVector class pennylane-lightning#985
• AQT: Delete references to the removed QubitStateVector class pennylane-aqt#77
• Qulacs: Delete references to the removed QubitStateVector class pennylane-qulacs#83
• Qiskit: Delete references to the removed QubitStateVector class pennylane-qiskit#601
• Cirq: Delete references to the removed QubitStateVector class pennylane-cirq#203

No references found in,

• QML

[sc-77482]

[lillian542]

🎉

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.29%. Comparing base (bf03136) to head (257b2fe).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6525      +/-   ##
==========================================
- Coverage   99.30%   99.29%   -0.01%     
==========================================
  Files         454      454              
  Lines       43269    43262       -7     
==========================================
- Hits        42967    42959       -8     
- Misses        302      303       +1     

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