RFR: 8262729: Cleanup OpenGL references from Metal implementation

[Ajit Ghaisas]

Cleaned up erroneous OpenGL references from Metal implementation.

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Commit messages:
 - clean up ogl references

Changes: https://git.openjdk.java.net/lanai/pull/206/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=206&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262729
  Stats: 19 lines in 5 files changed: 0 ins; 9 del; 10 mod
  Patch: https://git.openjdk.java.net/lanai/pull/206.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/206/head:pull/206

PR: https://git.openjdk.java.net/lanai/pull/206