RFR: JDK-8300910: Remove metaprogramming/integralConstant.hpp

[Justin King]

Code cleanup of pre-C++11 <type_traits> implementations.

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Commit messages:
 - Remove metaprogramming/integralConstant.hpp

Changes: https://git.openjdk.org/jdk/pull/12149/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12149&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300910
  Stats: 109 lines in 8 files changed: 10 ins; 64 del; 35 mod
  Patch: https://git.openjdk.org/jdk/pull/12149.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12149/head:pull/12149

PR: https://git.openjdk.org/jdk/pull/12149