Makefile cleanup and closing "forgot about new submodule" gaps

[Groxx]

Contains a few things, and will need to rebase on #6938 but:

• deleted the commented-out "copyright" stuff
• switched some simpler for loops over to $(foreach ...) which are a bit easier to read, and print more nicely with V=1 (you can see each fully-formed command as it is run, rather than one big for-loop for all steps)
  • it may not be a great option for complex stuff, as it seems like it can't blend newlines into the V=1 output. but it seems probably worth it for essentially-single-line stuff, and arguably anything larger deserves to be in a separate script for readability anyway...
• made some more helper-vars for "all submodules" and similar
• switched some "./..." and "depends on some/go.mod" over to the helper vars, so they now check everything rather than just one or two

I've re-checked several times but I'm not actually confident that this plugs all the "we added a new submodule and forgot to check in X" gaps... but it should be an improvement anyway.

[3vilhamster]

Look good.
So giventhis change - we will also need a
make prerelease v1.2.3-prerelease
and
make release v1.2.3
which should create all appropriate tags.

[Groxx]

Look good. So given this change - we will also need a make prerelease v1.2.3-prerelease and make release v1.2.3 which should create all appropriate tags.

yea, I'm thinking of making an interactive make release script, since there are a couple steps to it, and make release v1.2.3 isn't really feasible with make.

probably not too hard, and definitely seems worth it since we need to make N tags.

[3vilhamster]

Script for submodules release:
#6954