chore: drop deprecated Item class

[artemkurylo]

Drop deprecated Item class.

This class isn't used anymore and was deprecated along with drop of PHP 7.4. As a destructive example of it's presence, one of the projects that I'm working on tries to load every file from vendor directory into the memory and this class breaks it, because it doesn't comply with CacheItemInterface interface (missing return types, which results in a fatal error).

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[bshaffer]

As long as we support psr/cache: ^2.0, we need these item classes

google-auth-library-php/composer.json

Line 17 in 1277062

"psr/cache": "^2.0||^3.0"

[artemkurylo]

Ah, didn't notice it, makes sense. Thanks for taking a look.
Then we can close this one until team decides to drop the support for it.