Remove outdated IndirectlyMutableLocals

`MaybeMutBorrowedLocals` serves the same purpose and has a better name.

Author: ecstatic-morse

src/librustc_mir/dataflow/impls/indirect_mutation.rs

@@ -20,11 +20,9 @@ use super::drop_flag_effects_for_location;
 use super::on_lookup_result_bits;
 
 mod borrowed_locals;
-mod indirect_mutation;
 mod storage_liveness;
 
 pub use self::borrowed_locals::*;
-pub use self::indirect_mutation::IndirectlyMutableLocals;
 pub use self::storage_liveness::*;
 
 pub(super) mod borrows;