Remove unused variables and correct queueDepth default in IBM MQ scaler

[rickbrouwer]

• The current documentation states that the default queueDepth is 5, while the code default is 20. The documentation will be updated to reflect the correct default value of 20, aligning it with the code.
• The queueManager parameter is currently checked to see if it's filled, but it's not used elsewhere in the code. This unused code is removed. The documentation is updated accordingly.
• The parameter tlsDisabled is removed. All other scalers use the parameter unsafeSsl. To maintain consistency across the other scalers, the code related to tlsDisabled is removed, as unsafeSsl already handles this functionality.
• Finally, some minor adjustments to the documentation to keep the formatting the same.

Checklist

• Commits are signed with Developer Certificate of Origin (DCO)

Fixes #6033

[github-actions]

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