Remove deprecated XLAStatsMonitor

[ankitaS11]

What does this PR do?

Part of #12521.

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[akihironitta]

@ankitaS11 Thank you for working on this! Could you remove the following occurrences in the documentation?

./docs/source/extensions/callbacks.rst:109:    XLAStatsMonitor
./docs/source/api_references.rst:102:    XLAStatsMonitor

[awaelchli]

@ankitaS11 ping us if you need help resolving conflicts or addressing #12688 (review) :) Happy to help!

[ankitaS11]

@ankitaS11 Thank you for working on this! Could you remove the following occurrences in the documentation?

./docs/source/extensions/callbacks.rst:109:    XLAStatsMonitor
./docs/source/api_references.rst:102:    XLAStatsMonitor

Thanks @akihironitta, I have made the changes in the recent commit.

[rohitgr7]

thank you :)

[akihironitta]

@ankitaS11 Thank you :) LGTM!