Remove 'Limitations' from the reference guide

[emmurphy1]

In August 2022, as part of issue 200 the following guidance was added to the Modular Documentation Reference Guide:

Limitations
This section is optional and not used often. If there are any limitations that affect the procedure, list them in this section. Use a bulleted list for limitations and the plural heading Limitations, even if your procedure only has a single limitation.

This section was not added to the templates because the committee agreed that this is an uncommon request.

Because DITA does not have an equivalent element in the task DTD file, we need to remove this section from the reference guide.

#241

[maximiliankolb]

@aneta-petrova Is there a public list of allowed headings?

[aneta-petrova]

@maximiliankolb The headings in the templates are the ones supported for DITA migration: https://github.com/redhat-documentation/modular-docs/blob/main/modular-docs-manual/files/TEMPLATE_PROCEDURE_doing-one-procedure.adoc?plain=1