RFR: 8266789: devirtualize find_node and remove of LinkedList

[Xin Liu]

Devirtualize find, find_node and remove. This patch make both LinkedListImpl
and SortedLinkedList more generic. If the client doesn't use those member functions,
it's not necessary to define equals() for the user-defined class E.

Remove those 3 member functions from the pure interface LinkedList. subclasses
implement them using regular member functions.

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Commit messages:
 - 8266789: devirtualize find_node and remove of LinkedList

Changes: https://git.openjdk.java.net/jdk/pull/3944/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3944&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266789
  Stats: 83 lines in 2 files changed: 68 ins; 7 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3944.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3944/head:pull/3944

PR: https://git.openjdk.java.net/jdk/pull/3944