[jnigen] Remove C-based bindings #139

Job	Run time
analyze_jni	52s
build_jni_example_android	3m 17s
analyze_jnigen (stable)	37s
build_jni_example_linux	1m 30s
build_jni_example_windows	3m 0s
run_pdfbox_example_linux	2m 5s
test_jnigen_windows_minimal	6m 37s
test_jnigen (ubuntu-latest, stable)	8m 3s
test_jnigen_macos_minimal	5m 49s
test_jnigen (ubuntu-latest, beta)	6m 58s
test_jni_macos_minimal	2m 46s
test_jni_windows_minimal	3m 30s
test_jni	1m 48s
coveralls_finish	3s
	46m 55s

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