C#: Address review comment.

Author: michaelnebel

csharp/ql/src/Telemetry/ExternalApi.qll

@@ -5,7 +5,6 @@ private import dotnet
 private import semmle.code.csharp.dispatch.Dispatch
 private import semmle.code.csharp.dataflow.ExternalFlow
 private import semmle.code.csharp.dataflow.FlowSummary
-private import semmle.code.csharp.dataflow.internal.DataFlowImplCommon as DataFlowImplCommon
 private import semmle.code.csharp.dataflow.internal.DataFlowPrivate
 private import semmle.code.csharp.dataflow.internal.DataFlowDispatch as DataFlowDispatch
 private import semmle.code.csharp.dataflow.internal.FlowSummaryImpl as FlowSummaryImpl