RFR: 8265688: Unused ciMethodType::ptype_at should be removed

[Tobias Hartmann]

On Fri, 16 Dec 2022 10:28:09 GMT, Damon Fenacci <duke at openjdk.org> wrote:

> `ciMethodType::ptype_at` method is not used.
> 
> Removing it.

Looks good and trivial.

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Marked as reviewed by thartmann (Reviewer).

PR: https://git.openjdk.org/jdk/pull/11708