RFR: 6897: Remove unused javax imports

[Jie Kang]

JMC seemed to run fine with this patch. I was able to use the MXBeanBrowser, dump a flight recording of JMC and view
the flight recording.

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Commit messages:
 - 6897: Remove unused javax imports

Changes: https://git.openjdk.java.net/jmc/pull/106/files
 Webrev: https://webrevs.openjdk.java.net/jmc/106/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6897
  Stats: 4 lines in 2 files changed: 0 ins; 3 del; 1 mod
  Patch: https://git.openjdk.java.net/jmc/pull/106.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/106/head:pull/106

PR: https://git.openjdk.java.net/jmc/pull/106