Remove useless DumperCommonContext.targetTableColumnsMap #7644

Job	Run time
Import Global Environment / init-environment	4s
E2E - Agent with MySQL (proxy, tracing, jaeger)	10m 22s
E2E - Agent with MySQL (proxy, tracing, zipkin)	6m 9s
E2E - Agent with MySQL (proxy, metrics, prometheus)	7m 43s
E2E - Agent with MySQL (proxy, logging, file)	7m 43s
E2E - Agent with MySQL (jdbc, logging, file)	5m 59s
E2E - Agent with MySQL (jdbc, metrics, prometheus)	8m 50s
E2E - Agent with MySQL (jdbc, tracing, jaeger)	5m 56s
E2E - Agent with MySQL (jdbc, tracing, zipkin)	7m 50s
	1h 0m 36s

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