Update fff module tests

[yperess]

1. Remove the module tests (they're no longer needed since upstream FFF runs better CI now)
2. Update the header to match the pending PR at Support custom function signatures meekrosoft/fff#113

[zephyrbot]

The following west manifest projects have been modified in this Pull Request:

Name	Old Revision	New Revision	Diff
fff	zephyrproject-rtos/fff@6ce5ba2 (zephyr)	N/A	N/A

Note: This message is automatically posted and updated by the Manifest GitHub Action.

[yperess]

Failed compliance check is a false positive, the () cannot be moved closed to RETURN otherwise the macro expansion will treat RETURN as a macro function

[yperess]

@carlescufi what do you think of this? The CI on fff has been updated to use github actions so we also will be running those on our fork (once that PR merges) but we have a chicken & egg issue that I can't merge those changes without rolling back the additional commit that allowed us to run the fff tests on our CI. What I'd like to do:

1. Merge this commit to remove FFF from the CI of this repo
2. Roll back Add support for Zephyr fff#1
3. Pull all the upstream changes from https://github.com/meekrosoft/fff
4. Update the CI to just run a diff between the fff.h in our fork vs this repo (they should always match)

[carlescufi]

@carlescufi what do you think of this? The CI on fff has been updated to use github actions so we also will be running those on our fork (once that PR merges) but we have a chicken & egg issue that I can't merge those changes without rolling back the additional commit that allowed us to run the fff tests on our CI. What I'd like to do:

1. Merge this commit to remove FFF from the CI of this repo
2. Roll back Add support for Zephyr fff#1
3. Pull all the upstream changes from https://github.com/meekrosoft/fff
4. Update the CI to just run a diff between the fff.h in our fork vs this repo (they should always match)

I have no objections with the proposed plan, but I'd like @stephanosio to weigh in on it as well.

[stephanosio]

• Merge this commit to remove FFF from the CI of this repo
• Roll back Add support for Zephyr fff#1
• Pull all the upstream changes from https://github.com/meekrosoft/fff
• Update the CI to just run a diff between the fff.h in our fork vs this repo (they should always match)

As long as the "roll back" and the "pull" are done in a non-destructive way (i.e. no force push), no objections. It is important that the commit(s) that are referenced by previous Zephyr releases are valid.

[yperess]

• Merge this commit to remove FFF from the CI of this repo
• Roll back Add support for Zephyr fff#1
• Pull all the upstream changes from https://github.com/meekrosoft/fff
• Update the CI to just run a diff between the fff.h in our fork vs this repo (they should always match)

As long as the "roll back" and the "pull" are done in a non-destructive way (i.e. no force push), no objections. It is important that the commit(s) that are referenced by previous Zephyr releases are valid.

Yup, that's exactly what I had in mind, the PR is ready to go at https://github.com/zephyrproject-rtos/fff/pull/2/commits. You can see there that the first commit is a revert then a fetch from upstream.