Remove deprecated pennylane code

[mudit2812]

As name says. I've also temporarily added a warning filter to promote PennyLaneDeprecationWarnings to errors. I'll remove it once CI passes in this PR. Removed.

[mudit2812]

Proof of success here. The reference to qml._device.DeviceError has now been fixed as well, and the BasisStatePreparation warning is coming from tests, not from catalyst, so I'm leaving it as is. Going to remove the warning to error promotion now.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.86%. Comparing base (9a3e64b) to head (2d2a7e9).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1168   +/-   ##
=======================================
  Coverage   97.86%   97.86%           
=======================================
  Files          76       76           
  Lines       10807    10808    +1     
  Branches     1281     1281           
=======================================
+ Hits        10576    10577    +1     
  Misses        179      179           
  Partials       52       52           

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[mudit2812]

[sc-73914]

[dime10]

and the BasisStatePreparation warning is coming from tests, not from catalyst, so I'm leaving it as is. Going to remove the warning to error promotion now.

What do you mean by this? Ideally we don't want warnings in our tests either :)

[erick-xanadu]

Are broadcast templates being deprecated? Why don't we just remove the tests?

[mudit2812]

and the BasisStatePreparation warning is coming from tests, not from catalyst, so I'm leaving it as is. Going to remove the warning to error promotion now.

What do you mean by this? Ideally we don't want warnings in our tests either :)

@dime10 The warning is coming from the testing of the BasisStatePreparation template, which is deprecated. The catalyst codebase doesn't create BasisStatePreparation anywhere except for that one test. I'll add a warning suppression regardless.

Are broadcast templates being deprecated? Why don't we just remove the tests?

@erick-xanadu , I think it makes sense to keep the tests there. While broadcast is deprecated, it's still present, so better safe than sorry.