Integrated: 8260000: Remove JNF_COCOA_ENTER/EXIT usage from MTLGraphicsConfig.m

[Ajit Ghaisas]

Usage of JNF_COCOA_ENTER/EXIT was replaced in Lanai code-base under JDK-8259939, but fix of JDK-8258754 has introduced an instance in MTLGraphicsConfig.m. It needs to be replaced.

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Commit messages:
 - remove JNF_COCOA_* macro usage

Changes: https://git.openjdk.java.net/lanai/pull/156/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=156&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260000
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/lanai/pull/156.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/156/head:pull/156

PR: https://git.openjdk.java.net/lanai/pull/156