RFR: 8280496: Remove unused G1PageBasedVirtualSpace::pretouch_internal

[Kim Barrett]

Please review this trivial change to remove an unused function.

Testing:
mach5 tier1

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Commit messages:
 - remove unused pretouch_internal

Changes: https://git.openjdk.java.net/jdk/pull/7186/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7186&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280496
  Stats: 12 lines in 2 files changed: 0 ins; 10 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7186.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7186/head:pull/7186

PR: https://git.openjdk.java.net/jdk/pull/7186