RFR: 8255721: Remove no-op clean_weak_method_links methods [v2]

[Claes Redestad]

> ProfileData:: and DataLayout::clean_weak_method_links are both virtual but empty methods with no overrides, so removing them and simplifying MethodData::clean_weak_method_links should be a minor clean-up and possibly speed-up redefinition a notch.

Claes Redestad has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into methoddata_cleanup
 - Remove undefined declaration
 - Clean-up no-op clean_weak_method_links

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/990/files
  - new: https://git.openjdk.java.net/jdk/pull/990/files/4d5c18f4..653a325f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=990&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=990&range=00-01

  Stats: 4 lines in 2 files changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/990.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/990/head:pull/990

PR: https://git.openjdk.java.net/jdk/pull/990