Remove qml.queuing.Queue class

[albi3ro]

The qml.queuing.Queue class is a vestigial holdover from the early implementation that never ended up being used in anything. This PR removes this object and it's unit tests.

[github-actions]

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Please edit doc/releases/changelog-dev.md with:

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[codecov]

Codecov Report

Merging #2599 (ba53d05) into master (a61e25a) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2599   +/-   ##
=======================================
  Coverage   99.58%   99.59%           
=======================================
  Files         243      243           
  Lines       19589    19630   +41     
=======================================
+ Hits        19508    19550   +42     
+ Misses         81       80    -1     

Impacted Files	Coverage Δ
pennylane/math/single_dispatch.py	98.84% <100.00%> (+0.02%)	⬆️
pennylane/operation.py	96.83% <100.00%> (+0.10%)	⬆️
pennylane/ops/channel.py	100.00% <100.00%> (ø)
pennylane/queuing.py	100.00% <100.00%> (+1.16%)	⬆️
pennylane/tape/tape.py	98.89% <100.00%> (+0.05%)	⬆️

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