RFR: 8255562: delete UseRDPCForConstantTableBase

[Xin Liu]

UseRDPCForConstantTableBase was a SPARC-exclusive flag. Sparc has been removed 
from hotspot, so remove this flag.

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Commit messages:
 - delete UseRDPCForConstantTableBase

Changes: https://git.openjdk.java.net/jdk/pull/949/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=949&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255562
  Stats: 4 lines in 2 files changed: 0 ins; 3 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/949.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/949/head:pull/949

PR: https://git.openjdk.java.net/jdk/pull/949