RFR: 8270838: Remove deprecated protected access members from DateTimeStringConverter

[Nir Lisker]

`protected` members were changed to package visibility.

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Commit messages:
 - Removes deprecated memebers

Changes: https://git.openjdk.java.net/jfx/pull/578/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=578&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270838
  Stats: 31 lines in 1 file changed: 0 ins; 25 del; 6 mod
  Patch: https://git.openjdk.java.net/jfx/pull/578.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/578/head:pull/578

PR: https://git.openjdk.java.net/jfx/pull/578