RFR: 8348830: LIBFONTMANAGER optimization is always HIGHEST

[Matthias Baesken]

In the makefile we reset LIBFONTMANAGER optimization, but is always set to HIGHEST so we can avoid the resetting.

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Commit messages:
 - JDK-8348830

Changes: https://git.openjdk.org/jdk/pull/23332/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23332&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348830
  Stats: 5 lines in 1 file changed: 0 ins; 3 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23332.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23332/head:pull/23332

PR: https://git.openjdk.org/jdk/pull/23332