RFR: 8253631: Remove unimplemented CompileBroker methods after JEP-165

[Aleksey Shipilev]

It would seem that JEP-175 implementation task (JDK-8137167) introduced declarations without any implementations in
CompilerBroker:

  static DirectivesStack* dirstack();
  static void set_dirstack(DirectivesStack* stack);
  static void print_directives(outputStream* st);

This can be cleaned up.

Testing:
  - [x] Linux x86_64 fastdebug build
  - [x] Text searches for `dirstack` and `print_directives` in `src/hotspot`

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Commit messages:
 - 8253631: Remove unimplemented CompileBroker methods after JEP-165

Changes: https://git.openjdk.java.net/jdk/pull/353/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=353&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253631
  Stats: 5 lines in 1 file changed: 0 ins; 5 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/353.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/353/head:pull/353

PR: https://git.openjdk.java.net/jdk/pull/353