RFR: 8251023: Clipping of Image doesnt work when Alpha composite is enabled in J2DDemo

[Denis Konoplev]

Remove extra alpha logic from isBlendingDisabled

Also, this fix helps with background problem in this issue https://bugs.openjdk.java.net/browse/JDK-8244727

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Commit messages:
 - 8251023: Clipping of Image doesnt work when Alpha composite is enabled in J2DDemo

Changes: https://git.openjdk.java.net/lanai/pull/97/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=97&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251023
  Stats: 26 lines in 5 files changed: 0 ins; 20 del; 6 mod
  Patch: https://git.openjdk.java.net/lanai/pull/97.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/97/head:pull/97

PR: https://git.openjdk.java.net/lanai/pull/97