api: Remove obsolete TODO in EquivalentAddressGroup#toString

Author: stagegrowth

api/src/main/java/io/grpc/EquivalentAddressGroup.java

@@ -113,7 +113,9 @@ public Attributes getAttributes() {
 
   @Override
   public String toString() {
-    // TODO(zpencer): Summarize return value if addr is very large
+    // EquivalentAddressGroup is intended to contain a small number of addresses for the same endpoint
+    // (e.g., IPv4/IPv6). Aggregating many groups into a single EquivalentAddressGroup is no longer done,
+    // so this no longer needs summarization.
     return "[" + addrs + "/" + attrs + "]";
   }