Revert "Merge branch 'gitlab-default-mr-template' into 'master'"

Description

This reverts !1797 (merged)

Unfortunately having the default MR template in .gitlab/merge_request_templates/Default.md doesn't work as I'd expected:

• When the default MR template is specified in the lscsoft/lalsuite project settings, this is always applied to any MR when you select lscsoft/lalsuite:master as the MR target branch
• When the default MR template is specified in .gitlab/merge_request_templates/Default.md, however, the template appears not to actually be applied in every case:
  • When I tried to create a merge request for a trivial empty branch - i.e. a branch identical to master - the template was applied.
  • When I tried to create a merge request for a non-trivial branch - i.e. different from master by a single commit - the template was not applied. Initially the MR description was set to the commit message from the single commit. But when I switched the target branch from master in the source repository to lscsoft/lalsuite:master, the default MR template was not applied; the MR description was still just the commit message.

So either this feature is not working as it should yet (as it was only recently introduced in GitLab 14.8) or else I'm not understanding how it's implemented.

So instead I've just copied the updated (following #447 (closed)) default MR template back into the project setting, and to avoid confusion am reverting this MR.

API Changes and Justification

Backwards Compatible Changes

• This change does not modify any class/function/struct/type definitions in a public C header file or any Python class/function definitions
• This change adds new classes/functions/structs/types to a public C header file or Python module

Backwards Incompatible Changes

• This change modifies an existing class/function/struct/type definition in a public C header file or Python module
• This change removes an existing class/function/struct/type from a public C header file or Python module

If any of the Backwards Incompatible check boxes are ticked please provide a justification why this change is necessary and why it needs to be done in a backwards incompatible way.

Review Status

N/A