Remove misleading comments for Span in trace.proto (#408)

opentelemetry/proto/trace/v1/trace.proto

@@ -74,13 +74,7 @@ message ScopeSpans {
   string schema_url = 3;
 }
 
-// Span represents a single operation within a trace. Spans can be
-// nested to form a trace tree. Spans may also be linked to other spans
-// from the same or different trace and form graphs. Often, a trace
-// contains a root span that describes the end-to-end latency, and one
-// or more subspans for its sub-operations. A trace can also contain
-// multiple root spans, or none at all. Spans do not need to be
-// contiguous - there may be gaps or overlaps between spans in a trace.
+// A Span represents a single operation performed by a single component of the system.
 //
 // The next available field id is 17.
 message Span {