sstable: strengthen assertion around mutual exclusion of seek optimiz…

…ations

Previously an assertion that the TrySeekUsingNext and monotonic bounds
optimizations could not simultaneously be active was disabled due to the
TestIterRandomizedMaybeFilteredKeys test that could violate the invariant. The
test has been removed (along with the method it was testing), so we can
now uncondtionally restore the invariant.

sstable/reader_iter_two_lvl.go

@@ -310,18 +310,9 @@ func (i *twoLevelIterator) SeekGE(
 		// i.topLevelIndex.Key().UserKey) <= 0, we are at the correct lower level
 		// index block. No need to reset the state of singleLevelIterator.
 		//
-		// Note that cases 1 and 2 never overlap, and one of them must be true,
-		// but we used to have some test code (TestIterRandomizedMaybeFilteredKeys)
-		// that set both to true, so we fix things here and then do an invariant
-		// check.
-		//
+		// Note that cases 1 and 2 never overlap, and one of them must be true.
 		// This invariant checking is important enough that we do not gate it
 		// behind invariants.Enabled.
-		if i.boundsCmp > 0 {
-			// TODO(sumeer): fix now that TestIterRandomizedMaybeFilteredKeys does
-			// nnot exist.
-			flags = flags.DisableTrySeekUsingNext()
-		}
 		if i.boundsCmp > 0 == flags.TrySeekUsingNext() {
 			panic(fmt.Sprintf("inconsistency in optimization case 1 %t and case 2 %t",
 				i.boundsCmp > 0, flags.TrySeekUsingNext()))