Go/Java: fix miscellaneous trivial issues highlighted by ql-for-ql

[owen-mc]

All trivial changes, except one renaming of a predicate, but it's in experimental so we don't expect anyone to be relying on it.

[Copilot]

Pull request overview

This PR addresses trivial code quality issues identified by ql-for-ql analysis, focusing on removing redundant code, improving documentation, and standardizing formatting.

• Removes redundant code constructs (unused imports, unnecessary exists clauses, and redundant constructors)
• Renames a predicate in experimental code to follow QL naming conventions
• Improves comment clarity and formatting consistency in query metadata

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
go/ql/test/library-tests/semmle/go/dataflow/GlobalVariableSideEffects/Flows.ql	Removes redundant exists(src) and clause that serves no purpose
go/ql/src/experimental/frameworks/DecompressionBombsCustomizations.qll	Updates comment to be more concise and accurate for the class description
go/ql/src/experimental/CWE-918/validator.qll	Renames predicate from getTagByKeyValue to hasTagKeyValue to follow QL naming conventions
go/ql/src/Security/CWE-020/UntrustedDataToUnknownExternalAPI.ql	Splits tags metadata onto separate lines for better formatting
go/ql/src/Security/CWE-020/UntrustedDataToExternalAPI.ql	Splits tags metadata onto separate lines for better formatting
go/ql/lib/semmle/go/dataflow/internal/DataFlowNodes.qll	Removes unused private import of Private module
go/ql/lib/semmle/go/dataflow/GlobalValueNumbering.qll	Removes redundant constructor that adds no value

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