RFR: JDK-8308028 Replace more uses of System.getProperty("os.name") with PlatformUtil calls

[Carl Döbbelin]

replaced implementation of OS checks in HostUtils with calls of PlatformUtil

-------------

Commit messages:
 - replaced implementation of OS checks in HostUtils with calls of PlatformUtil

Changes: https://git.openjdk.org/jfx/pull/1134/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1134&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308028
  Stats: 6 lines in 1 file changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jfx/pull/1134.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1134/head:pull/1134

PR: https://git.openjdk.org/jfx/pull/1134