RFR: 8271737: Only normalize the cached user.dir property once

[Evgeny Astigeevich]

The change completes the fix of [JDK-8198997](https://bugs.openjdk.java.net/browse/JDK-8198997) which has added normalisation in a constructor but not removed it from the get method.

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Commit messages:
 - 8271737: Only normalize the cached user.dir property once

Changes: https://git.openjdk.java.net/jdk/pull/5850/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5850&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271737
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5850.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5850/head:pull/5850

PR: https://git.openjdk.java.net/jdk/pull/5850