RFR: 8276179 removing unused font code - isInstalledFont

[Florian Kirmaier]

removing dead code.
When looking into the font code, I've noticed that this code is no longer used, so I thought I should make a PR with a minor cleanup.

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Commit messages:
 - JDK-8276179

Changes: https://git.openjdk.java.net/jfx/pull/658/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=658&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276179
  Stats: 34 lines in 2 files changed: 0 ins; 34 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/658.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/658/head:pull/658

PR: https://git.openjdk.java.net/jfx/pull/658