Fixes absl include (removes third_party/ prefix).

Author: mmoffitt

src/sweeper.cc

@@ -22,7 +22,7 @@ limitations under the License.
 #include <vector>
 
 #include "absl/container/btree_set.h"
-#include "third_party/absl/container/flat_hash_set.h"
+#include "absl/container/flat_hash_set.h"
 #include "minimalloc.h"
 
 namespace minimalloc {