SQL: Drop equals and hashCode from FunctionDefinition (elastic/x-pack-elasticsearch#3444)

They aren't used and they don't look right.

Original commit: elastic/x-pack-elasticsearch@4d07f66f0f

sql/server/src/main/java/org/elasticsearch/xpack/sql/expression/function/FunctionDefinition.java

@@ -50,27 +50,6 @@ public class FunctionDefinition {
         return builder;
     }
 
-    @Override
-    public int hashCode() {
-        return Objects.hash(clazz);
-    }
-
-    @Override
-    public boolean equals(Object obj) {
-        if (this == obj) {
-            return true;
-        }
-
-        if (obj == null || getClass() != obj.getClass()) {
-            return false;
-        }
-
-        FunctionDefinition other = (FunctionDefinition) obj;
-        return Objects.equals(clazz, other.clazz) &&
-                Objects.equals(name, other.name) &&
-                Objects.equals(aliases, aliases);
-    }
-
     @Override
     public String toString() {
         return format(Locale.ROOT, "%s(%s)", name, aliases.isEmpty() ? "" : aliases.size() == 1 ? aliases.get(0) : aliases );