chore(shell-api): remove dropped timeseries collStats field from test MONGOSH-1763 (#1956)

This field is gone from most recent server versions. It's probably safe to just
ignore this field altogether at this point instead of performing server version
detection and adjusting the list of expected keys to account for that.

Author: addaleax

packages/shell-api/src/integration.spec.ts

@@ -940,7 +940,6 @@ describe('Shell API (integration)', function () {
             'numBucketsClosedDueToCount',
             'numBucketsClosedDueToSize',
             'numBucketsClosedDueToTimeForward',
-            'numBucketsClosedDueToTimeBackward',
             'numBucketsClosedDueToMemoryThreshold',
             'numCommits',
             'numWaits',