infra: remove generate contrib workflows from core #644

Job	Run time
opentelemetry-api	42s
opentelemetry-getting-started	55s
opentelemetry-proto-protobuf5	30s
opentelemetry-sdk	45s
opentelemetry-semantic-conventions	35s
opentelemetry-exporter-opencensus	43s
opentelemetry-exporter-otlp-combined	58s
opentelemetry-exporter-otlp-proto-common	40s
opentelemetry-exporter-otlp-proto-grpc	48s
opentelemetry-exporter-otlp-proto-http	41s
opentelemetry-exporter-prometheus	36s
opentelemetry-exporter-zipkin-combined	39s
opentelemetry-exporter-zipkin-json	34s
opentelemetry-exporter-zipkin-proto-http	39s
opentelemetry-opencensus-shim	36s
opentelemetry-opentracing-shim	37s
opentelemetry-propagator-jaeger	36s
opentelemetry-test-utils	37s
opentelemetry-propagator-b3	39s
	12m 50s

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