RFR: 8360303: Remove two unused invoke files

[Chen Liang]

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: jdk/java/lang/invoke

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Commit messages:
 - Remove two useless invoke files

Changes: https://git.openjdk.org/jdk/pull/25944/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25944&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8360303
  Stats: 79 lines in 4 files changed: 0 ins; 77 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/25944.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25944/head:pull/25944

PR: https://git.openjdk.org/jdk/pull/25944