RFR: 8263821: Remove unused MethodTypeForm canonicalization codes

[Claes Redestad]

MethodTypeForm.INTS, LONGS and RAW_RETURN are effectively unused. This removes these canonicalization codes and cleans up related code.

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

Commit messages:
 - Minor simplifications
 - Remove unused MethodTypeForm canonicalization codes

Changes: https://git.openjdk.java.net/jdk/pull/3075/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3075&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263821
  Stats: 45 lines in 2 files changed: 0 ins; 35 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3075.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3075/head:pull/3075

PR: https://git.openjdk.java.net/jdk/pull/3075