Remove cloud result handler

[cicdw]

Thanks for contributing to Prefect!

Please describe your work and make sure your PR:

• adds new tests (if appropriate)
• updates CHANGELOG.md (if appropriate)
• updates docstrings for any new functions or function arguments, including docs/outline.toml for API reference docs (if appropriate)

Note that your PR will not be reviewed unless all three boxes are checked.

What does this PR change?

Removes the CloudResultHandler entirely

Closes #1197

[joshmeek]

Can you also remove result_handler = "${cloud.api}/result-handler" from the config

[codecov]

Codecov Report

Merging #1198 into master will decrease coverage by 0.04%.
The diff coverage is 100%.

[cicdw]

@joshmeek good catch - done.