Update deprecation and removal templates for correct labels

What does this MR do and why?

Describe in detail what your merge request does and why.

When creating removal notices, using the existing Removals MR template causes a Danger bot error such as the following:

This is because the label typemaintenance is added without a corresponding sub-type.

Looking at the Work type classification documentation, it would appear that this should be classified as maintenanceremoval.

I have also updated the Deprecations MR template to use the maintenanceremoval label as it does not appear that the maintenancerefactor sub-classification was correct based on the above documentation.

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