RFR: 8256213: Remove os::split_reserved_memory

[Yumin Qi]

Hi, Please review 
  This is the second step for removing problematic os::split_reserved_memory on Windows. The first step has been accomplished under bug 8255917 (https://bugs.openjdk.java.net/browse/JDK-8255917).
  This step remove the function split_reserved_memory which no longer be called after first step.

Tests: tier1-4

Thanks
Yumin

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Commit messages:
 - 8256213: Remove os::split_reserved_memory

Changes: https://git.openjdk.java.net/jdk/pull/1825/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1825&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256213
  Stats: 70 lines in 6 files changed: 0 ins; 63 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1825.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1825/head:pull/1825

PR: https://git.openjdk.java.net/jdk/pull/1825