Revert "Fix Issue 21456 - std.format does not accept enum member with string base type as template parameter"

[berni44]

Reverts #8029

See discussion there and discussion in the forum.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✗	21456	normal	std.format does not accept enum member with string base type as template parameter

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 + phobos#8057"

[RazvanN7]

cc @andralex