Remove deprecated paul_mult and pauli_mult_with_phase

[astralcai]

Context:
Complete the deprecation cycle for qml.pauli.pauli_mult and qml.pauli.pauli_mult_with_phase

Description of the Change:
qml.pauli.pauli_mult and qml.pauli.pauli_mult_with_phase are now removed. Instead, you should use qml.simplify(qml.prod(pauli_1, pauli_2)) to get the reduced operator.

>>> op = qml.simplify(qml.prod(qml.PauliX(0), qml.PauliZ(0)))
>>> op
-1j*(PauliY(wires=[0]))
>>> [phase], [base] = op.terms()
>>> phase, base
(-1j, PauliY(wires=[0]))

Related Shortcut Issues:
[sc-58145]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.63%. Comparing base (e475db3) to head (c0c20e5).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5324      +/-   ##
==========================================
- Coverage   99.64%   99.63%   -0.01%     
==========================================
  Files         401      401              
  Lines       37294    36976     -318     
==========================================
- Hits        37160    36841     -319     
- Misses        134      135       +1     

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[lillian542]

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