Remove unused method

Author: mcculls

internal-api/src/main/java/datadog/trace/bootstrap/instrumentation/api/TagContext.java

@@ -176,15 +176,6 @@ public void putTag(final String key, final String value) {
     this.tags.set(key, value);
   }
 
-  public void putTagIfAbsent(final String key, final String value) {
-    if (this.tags == null) {
-      this.tags = TagMap.create(4);
-    }
-    if (!this.tags.containsKey(key)) {
-      this.tags.set(key, value);
-    }
-  }
-
   @Override
   public final int getSamplingPriority() {
     return samplingPriority;