Update documentation to omit empty attributes (#15465)

Author: cleptric

develop-docs/sdk/telemetry/spans/span-protocol.mdx

@@ -165,7 +165,7 @@ Attributes are stored as key-value pairs where each value is an object with type
 #### Common Attribute Keys
 
 All attributes mentioned below must be attached to every span being emitted from the SDK, depending on the platform.
-Empty attributes must be emitted.
+Empty attributes must be omitted.
 
 | Attribute Key | Type | Description |
 |---------------|------|-------------|