RFR: JDK-8300264: Remove metaprogramming/isPointer.hpp

[Justin King]

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

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Commit messages:
 - Remove metaprogramming/isPointer.hpp

Changes: https://git.openjdk.org/jdk/pull/12041/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12041&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300264
  Stats: 106 lines in 5 files changed: 2 ins; 95 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/12041.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12041/head:pull/12041

PR: https://git.openjdk.org/jdk/pull/12041