OPENNLP-1687: Remove quotes around $HEAP in opennlp tools shell script

[chenrui333]

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Previously, $HEAP was wrapped in quotes when passed to java, causing an empty or incorrect argument to be parsed, which could trigger a “Could not find or load main class” error (e.g., in Homebrew environments). By removing the quotes, $HEAP is now passed correctly, ensuring Java recognizes the classpath and preventing the ClassNotFoundException. This also allows multiple or custom JVM arguments (e.g., -Xmx512m -Xms256m) to be supplied through $JAVA_HEAP if desired.

relates to Homebrew/homebrew-core#202547

[mawiesne]

@chenrui333 Thx for finding this and providing a PR.