Delete leftover assignment from facebook#18384

This assignment should have been deleted in facebook#18384. It was deleted in
the other branches, but I missed this one. About to open a PR that
includes a test that covers this branch.

Author: acdlite

Diff for: packages/react-reconciler/src/ReactFiberBeginWork.js

@@ -1937,7 +1937,6 @@ function updateSuspenseComponent(
           currentPrimaryChildFragment.childExpirationTime,
           renderExpirationTime,
         );
-        primaryChildFragment.childExpirationTime = NoWork;
         // Skip the primary children, and continue working on the
         // fallback children.
         workInProgress.memoizedState = SUSPENDED_MARKER;