[Chapel Merge] Unset unwanted `CHPL_LAUNCHER` in multilocale test configs

Branch: refs/heads/main
Revision: 1b8ea37ac9116dc42398a4394bf5237a1d87f470
Author: arifthpe
Link: Unset unwanted `CHPL_LAUNCHER` in multilocale test configs by arifthpe · Pull Request #28529 · chapel-lang/chapel · GitHub
Log Message:
Unset unwanted CHPL_LAUNCHER in multilocale test configs (#28529)

Unset CHPL_LAUNCHER in multilocale test configs which began failing
after sourceing common-localnode-paratest.bash, which sets
CHPL_LAUNCHER=none.

I referenced test-gasnet.darwin.bash doing so as a justification for
this.

Follow up to Increase nightly testing parallelism by arifthpe · Pull Request #28525 · chapel-lang/chapel · GitHub.

[reviewed by @jabraham17, thanks!]

Compare: Comparing 2e6ef2675cc4c6a02c4d9e8396b762526f14d119...47ffee4334d2bae2af1d538018d67c1d3019a04a · chapel-lang/chapel · GitHub

Diff:
M util/cron/test-gasnet.c-backend.bash
M util/cron/test-gasnet.quickstart.bash
M util/cron/test-ml-memleaks.bash
https://github.com/chapel-lang/chapel/pull/28529.diff