[CI][Crossbow] Fix or delete fuzzit jobs

[asfimport]

Not sure we need them now that we're using the OSS-Fuzz project, but they're broken. 

Reporter: Neal Richardson / @nealrichardson
Assignee: Antoine Pitrou / @pitrou

Related issues:

• [CI][Crossbow] NIghtly fuzzit build broken in docker-compose refactor (supercedes)
• [CI] Figure out how to run reliably the fuzzit task (supercedes)
• [C++][CI] Test the ported fuzzit integration image (supercedes)

PRs and other links:

• GitHub Pull Request #6328

_{Note: This issue was originally created as ARROW-7712. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
I think the fuzzit setup is handled by [~marco.neumann.by]. Personally I will focus on OSS-Fuzz.

[asfimport]

Marco Neumann / @crepererum:
@pitrou I think we should focus on a single solution. I don't have a very strong opinion on that. Fuzzit was nice because they approached me and offered their solution including some assistance, but OSS-fuzz is the de facto standard for OSS.

[asfimport]

Kouhei Sutou / @kou:
Issue resolved by pull request 6328
#6328