RFR: 8254966: Remove unused code from Matcher

[Claes Redestad]

These are unused:

interpreter_method_reg*
compiler_method_reg*
pd_implicit_null_fixup (only existed to workaround some Win95 issues)

Quite some code in the .ad files shook loose when removing these, so I will need some help verifying that the s390 and
ppc changes are fine.

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Commit messages:
 - Remove interpreter_method_reg from AD files, adjust parser
 - Clean out compiler_method_reg left-overs
 - Remove unused methods in matcher and corresponding code in ad files

Changes: https://git.openjdk.java.net/jdk/pull/723/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=723&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254966
  Stats: 273 lines in 11 files changed: 1 ins; 259 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/723.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/723/head:pull/723

PR: https://git.openjdk.java.net/jdk/pull/723