RFR: 8278047: Few javax/imageio test regressed after JDK-8262297 fix

[Jayathirth D V]

Looks like we have 8 test cases where we are trying to write 15bpp BMP images and after JDK-8262297 all of them are failing.
We need to update these test cases to not encode 15bpp BMP images or supporting 15bpp BMP images is valid use case. This needs more investigation. I am backing out changes done under JDK-8262297 for further analysis.

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Commit messages:
 - 8278047: Few javax/imageio test regressed after JDK-8262297 fix

Changes: https://git.openjdk.java.net/jdk/pull/6631/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6631&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278047
  Stats: 86 lines in 2 files changed: 0 ins; 84 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6631.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6631/head:pull/6631

PR: https://git.openjdk.java.net/jdk/pull/6631