OPENNLP-996: Remove heap memory settings from Opennlp-tools

[smarthi]

Thank you for contributing to Apache OpenNLP.

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to ensure the following steps have been taken:

For all changes:

• Is there a JIRA ticket associated with this PR? Is it referenced
  in the commit message?

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[coveralls]

Coverage remained the same at 51.754% when pulling d0dffce on smarthi:OPENNLP-996 into f2f987d on apache:master.

[smarthi]

Merging this now...

[kottmann]

+1 lgtm