remove cruft

Author: mbroadst

src/sessions.ts

@@ -793,16 +793,6 @@ function applySession(
     return;
   }
 
-  if (options) {
-    ReadPreference.translate(options);
-    // const readPreference = options.readPreference as ReadPreference;
-    // if (readPreference && !readPreference.equals(ReadPreference.primary)) {
-    //   return new MongoError(
-    //     `Read preference in a transaction must be primary, not: ${readPreference.mode}`
-    //   );
-    // }
-  }
-
   // `autocommit` must always be false to differentiate from retryable writes
   command.autocommit = false;