Avoid clearing span context tags upon export

Profiler may need the tags to determine span resource name for endpoint
aggregation: profiler keeps a reference on web span that was active when
each profiling sample is taken. Then during profile export, span tags
are used to determine endpoint. Endpoint cannot be determined right away
because sometimes tags necessary to determine endpoint are only set just
before span is finished.

Author: nsavoire

packages/dd-trace/src/span_processor.js

@@ -138,10 +138,6 @@ class SpanProcessor {
       }
     }
 
-    for (const span of trace.finished) {
-      span.context()._tags = {}
-    }
-
     trace.started = active
     trace.finished = []
   }