Remove header gerund rule from Vale

Remove the Vale rule regarding use of gerunds in headers

doc/.vale/gitlab/HeaderGerunds.yml

----
-# Suggestion: gitlab.HeaderGerunds
-#
-# Checks for headers that start with gerunds (ing words).
-# Related to: https://docs.gitlab.com/ee/development/documentation/structure.html
-#
-# For a list of all options, see https://errata-ai.gitbook.io/vale/getting-started/styles
-extends: substitution
-message: 'Can this header start with an imperative verb, instead of a gerund (ing word)?'
-link: https://docs.gitlab.com/ee/development/documentation/styleguide/#heading-titles
-level: suggestion
-scope: heading
-swap:
-  - '^\w*ing.*': 'Troubleshooting'