RFR: 1397: Skara doesn't handle tags with more than 4 digits in version number

[Erik Joelsson]

To be able to react to new tags, Skara needs to know how to parse our tag formats. For this we have the OpenJDKTag class. The current pattern for Verona based version numbers in this class is limited to tags with 4 digit version numbers. This becomes a problem when a JDK release uses more of the up to 7 possible version digits currently allowed in mainline since [JDK-8207849](https://bugs.openjdk.java.net/browse/JDK-8207849). 

This patch raises the limit to 7 digits to match what is currently possible in the JDK build. I'm also removing the redundant and incomplete "OpenJDKVersionPattern" which seemed to not serve any purpose as the existing OpenJFXVersionPattern covered everything for both JDK and JFX tags.

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Commit messages:
 - SKARA-1397

Changes: https://git.openjdk.java.net/skara/pull/1299/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1299&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1397
  Stats: 28 lines in 2 files changed: 24 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/skara/pull/1299.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1299/head:pull/1299

PR: https://git.openjdk.java.net/skara/pull/1299