BridgeJS: Fix unused variable warnings in JSGlueGen.swift #2224

Job	Run time
Build for native target (macos-15, Xcode_16.4)	3m 3s
build-examples	25m 51s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	4m 43s
check-bridgejs-generated	2m 49s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	17m 23s
format	32s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	13m 49s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	13m 46s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	2m 59s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	13m 12s
deploy-examples	9s
	1h 38m 16s

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