ENH Remove resources-dir config from composer.json

[GuySartorelli]

Parent issue

• Default resources folder to _resources silverstripe-framework#10399

[michalkleiner]

At first, I was alarmed why we were removing the config, then I had to go and check the parent issue and only there I find the default would change so the config won't be needed anymore if merged in the correct order. It might be worth updating the title of the follow-up PRs to that effect or at least the description of the code change.

[GuySartorelli]

This is in draft in part because I didn't notice the config wasn't meant to be removed until after I did most of the work. 😅
Pending clarification

[GuySartorelli]

To clarify: The config being removed from these composer.json files is correct.
The default is being changed in framework and in vendor-plugin.

I think this PR's title is correct.
The PRs for framework/vendor-plugin have been swapped out for the correct functionality change and the titles for those are correspondingly correct for the changes being made in those repos.