Remove empty test suite `tests/run-make-fulldeps`
After #109770, there were only a handful of tests left in the run-make-fulldeps suite.
As of #126111, there are no longer *any* run-make-fulldeps tests, so now we can:
- Remove the directory
- Remove related bootstrap/compiletest code
- Remove various other references in CI scripts and documentation.
By removing this suite, we also no longer need to worry about discrepancies between it and ui-fulldeps, and we don't have to worry about porting tests from Makefile to [rmake](https://github.com/rust-lang/rust/issues/121876) (or whether rmake even works with fulldeps).