RFR: 6462028: MaskFormatter API documentation refers to getDisplayValue

[Tejesh R]

MaskFormatter API doesn't have getDisplayValue method, hence removed from Documentation.

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Commit messages:
 - 6462028:MaskFormatter API documentation refers to getDisplayValue

Changes: https://git.openjdk.java.net/jdk/pull/6556/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6556&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-6462028
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6556.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6556/head:pull/6556

PR: https://git.openjdk.java.net/jdk/pull/6556