RFR: 8254246: SymbolHashMapEntry wastes space

[Coleen Phillimore]

The ConstantPool SymbolHashMapEntry is used by class file reconstitution, so the little wasted space doesn't make a difference, but it's fixed here.  Tested with tier1 and vmTestbase/nsk/{jdi,jvmti} tests.  Should be trivial.

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Commit messages:
 - 8254246: SymbolHashMapEntry wastes space

Changes: https://git.openjdk.java.net/jdk/pull/2228/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2228&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254246
  Stats: 4 lines in 1 file changed: 1 ins; 1 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2228.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2228/head:pull/2228

PR: https://git.openjdk.java.net/jdk/pull/2228