Remove in_band_lifetimes from rustc_infer

This crate actually had a typo `'ctx` in one of its functions:
```diff
-pub fn same_type_modulo_infer(a: Ty<'tcx>, b: Ty<'ctx>) -> bool {
+pub fn same_type_modulo_infer<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
```

compiler/rustc_infer/src/lib.rs

@@ -20,7 +20,6 @@
 #![feature(iter_zip)]
 #![feature(let_else)]
 #![feature(never_type)]
-#![feature(in_band_lifetimes)]
 #![feature(control_flow_enum)]
 #![feature(min_specialization)]
 #![feature(label_break_value)]