RFR: JDK-8299482: Remove metaprogramming/isIntegral.hpp

[Justin King]

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

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Commit messages:
 - Remove metaprogramming/isIntegral.hpp

Changes: https://git.openjdk.org/jdk/pull/11818/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11818&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299482
  Stats: 140 lines in 5 files changed: 3 ins; 123 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/11818.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11818/head:pull/11818

PR: https://git.openjdk.org/jdk/pull/11818