fix: delete GenericTypeEx trait

[jujube]

This way, the code is clearer and easier to understand.

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This change is 

[orizi]

Reviewable status: 0 of 5 files reviewed, 1 unresolved discussion (waiting on @jujube)

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crates/cairo-lang-sierra/src/extensions/types.rs line 20 at r1 (raw file):

    ) -> Result<Self::Concrete, SpecializationError>;

    fn specialize_by_id(

this change makes specialized_by_id be overridable - when it isn't designed to be.

Code quote:

 fn specialize_by_id(

[jujube]

The function of these two implementation methods is the same.
But the original implementation is not easy to understand.

[orizi]

this is the concept of an extension trait - there's no repeated implementation.

Reviewable status: 0 of 5 files reviewed, 1 unresolved discussion (waiting on @jujube)