Remove individuals from CODEOWNERS (#410)

Stop spamming Quigley and Grace 🙃 I have gotten their consent to do
this.
### Description

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Author: courtneyholcomb

.github/CODEOWNERS

@@ -13,4 +13,4 @@
 * @dbt-labs/semantic-layer
 
 # Parsing, validations, and protocols
-/dbt_semantic_interfaces/**  @dbt-labs/semantic-layer @QMalcolm @graciegoheen
+/dbt_semantic_interfaces/**  @dbt-labs/semantic-layer