RFR: 8360303: Remove two unused invoke files

[John R Rose]

On Mon, 23 Jun 2025 22:48:52 GMT, Chen Liang <liach at openjdk.org> wrote:

> sun.invoke.empty.Empty and java.lang.invoke.InvokeDynamic are useless remnants - Empty can be replaced by java.lang.Void, and InvokeDynamic was previously used as a stub for javac to compile signature polymorphic methods. They should be removed as a cleanup.
> 
> Testing: tier 1-3

Marked as reviewed by jrose (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/25944#pullrequestreview-2959269167