Remove unused UnitResult type.

Author: nnethercote

compiler/rustc_infer/src/infer/mod.rs

@@ -50,7 +50,6 @@ use snapshot::undo_log::InferCtxtUndoLogs;
 use tracing::{debug, instrument};
 use type_variable::TypeVariableOrigin;
 
-usecrate::infer::relate::RelateResult;
 usecrate::traits::{self,ObligationCause,ObligationInspector,PredicateObligation,TraitEngine};
 
 pubmod at;
@@ -76,7 +75,6 @@ pub struct InferOk<'tcx, T> {
 }
 pubtypeInferResult<'tcx,T> = Result<InferOk<'tcx,T>,TypeError<'tcx>>;
 
-pubtypeUnitResult<'tcx> = RelateResult<'tcx,()>;// "unify result"
 pubtypeFixupResult<T> = Result<T,FixupError>;// "fixup result"
 
 pub(crate)typeUnificationTable<'a,'tcx,T> = ut::UnificationTable<