Fix 21019 - Replace rm with rm_retry in shell scripts

[MoonlightSentinel]

CC @WalterBright

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21019	normal	Azure pipelines Windows_VisualD win32-ldc fails with Heisenbug

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#11380"

[MoonlightSentinel]

Explicitly sourceing for every POSTSCRIPT isn't pretty but they will be replaced anyway in the near future.

[WalterBright]

Thanks!