license-classification: Drop the redundant 'strong-copyleft' category

[fviernau]

The categories 'copyleft' and 'strong-copyleft' have identical semantics, while 'copyleft' has more usages and aligns with ScanCode's category name. So, align on using 'copyleft' as category for "Strong Copyleft" licenses.

Part of #59.

[sschuberth]

AFAIK, the most common terms for the "big three" license categories are "strong copyleft", "weak copyleft", and "permissive". While I agree that here "copyleft" and "strong copyleft" have identical semantics, I would have preferred to align on the more common "strong copyleft" term, and while at it also rename "copyleft-limited" to "weak-copyleft" (assuming that's what's mean with "copyleft-limited").

[fviernau]

AFAIK, the most common terms for the "big three" license categories are "strong copyleft", "weak copyleft", and "permissive". While I agree that here "copyleft" and "strong copyleft" have identical semantics, I would have preferred to align on the more common "strong copyleft" term, and while at it also rename "copyleft-limited" to "weak-copyleft" (assuming that's what's mean with "copyleft-limited").

This PR is in context of generating the license classification from ScanCode license database and using it in ORT config.
So, I prefer to align with the names of ScanCode.
Given that, do you agree?

[sschuberth]

Given that, do you agree?

I guess it's a bit weird for ScanCode to use those names; but yes, for the sake of easily generating the classifications, it make sense to use whatever the source of choice uses.