<i18n dev> RFR: 8296140: Drop unused field java.util.Calendar.DATE_MASK

[Andrey Turbanov]

There is no usages for this field. As it has the same value as `DAY_OF_MONTH_MASK` we can drop it.

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Commit messages:
 - [PATCH] Drop unused field java.util.Calendar.DATE_MASK

Changes: https://git.openjdk.org/jdk/pull/10888/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10888&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296140
  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10888.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10888/head:pull/10888

PR: https://git.openjdk.org/jdk/pull/10888