W-17013213 fix: add warning when nothing to delete

[WillieRuemmele]

What does this PR do?

if you project delete source on something that's forceignored, you can have a bad time
this makes you have less of a bad time, prints a warning

What issues does this PR fix or reference?

@W-17013213@

[shetzel]

QA
Try to delete an LWC tests dir. With the changes you see a warning like this:

Warning: Attempting to delete metadata that conflicts with a .forceignore entry: .../force-app/main/default/lwc/brokerCard/__tests__/brokerCard.test.js,.../force-app/main/default/lwc/brokerCard/__tests__/data
Update the .forceignore file and try again.
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