RFR: 8261268: LOAD_INSTANCE placeholders unneeded for parallelCapable class loaders

[Coleen Phillimore]

See CR for more details.  This optimizes some code for class loading.
Tested with tier1-6.

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Commit messages:
 - Make parallelCapable() classes not take LOAD_INSTANCE placeholder.

Changes: https://git.openjdk.java.net/jdk/pull/2469/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2469&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261268
  Stats: 84 lines in 3 files changed: 12 ins; 36 del; 36 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2469.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2469/head:pull/2469

PR: https://git.openjdk.java.net/jdk/pull/2469