Update Mavlink git repo, remove hot-patching of mavros and mavlink code

[amarburg]

Changes Made

This PR updates the current main which still builds mavros and mavlink from source .... with the understanding that it's not long for this world (Issue #324). But it un-breaks CI until that happens.

• Clones mavlink from https://github.com/ros2-gbp/mavlink-gbp-release.git rather than mavlink/mav-gdp-release.git. The latter is out of date.
• Removes the sed-based hot-patching of the Mavlink and Mavros code.

Associated Issues

Please provide a list of all open issues that this PR will close or contribute
toward closing.

• Fixes (just) [FEATURE]: Remove unnecessary modifications to MAVROS and source build #312

Notably, does not fix #324

[amarburg]

Depending on the state of #324 , this may be obsolete....

[evan-palmer]

Just need to revert the target organization in the build then this should be good to go.

[amarburg]

I'm still mystified at how I end up with such a long trail of commits. Let me do a little rebasing and I'll push a more surgical update.

[amarburg]

For those keeping track at home, I'm able to replicate the build error (ERROR: EOF) by upgrading docker buildx on the desktop from version 0.17.x to 'v0.19.2 1fc5647' (the latest version available for 24.04).

No solution yet...

[amarburg]

Appears to be an upstream change in the parser for docker-buildx v0.19.x (possibly related to the Release note for v0.19.1, though v0.19.1/v0.19.2 do not fix it).

These latest versions of buildx don't like the syntax *.cache-to= to unset the cache-to attribute. Trying various combinations of [], '' and "" didn't fix it.

As a hack, pin buildx to v0.18.0 in the Github workflow.

Added the fix to this PR rather than starting another because I'm not (much of) a sadist. Simple to cherry-pick the change into #324 if we want to abandon this PR.

[evan-palmer]

Thanks for working on this. I don't see any problem with pinning the version as a quick fix. Would you be willing to submit an issue so that we don't forget about that?