Remove 'speculative evaluation' of predicates

Performing 'speculative evaluation' introduces caching bugs that
cannot be fixed without invasive changes to projection.

Hopefully, we can win back most of the performance lost by
re-adding 'cache completion'

Fixes #90662

compiler/rustc_trait_selection/src/traits/project.rs

@@ -10,7 +10,6 @@ use super::PredicateObligation;
 use super::Selection;
 use super::SelectionContext;
 use super::SelectionError;
-use super::TraitQueryMode;
 use super::{
     ImplSourceClosureData, ImplSourceDiscriminantKindData, ImplSourceFnPointerData,
     ImplSourceGeneratorData, ImplSourcePointeeData, ImplSourceUserDefinedData,
@@ -946,27 +945,11 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
             };
 
             let mut deduped: SsoHashSet<_> = Default::default();
-            let mut canonical =
-                SelectionContext::with_query_mode(selcx.infcx(), TraitQueryMode::Canonical);
-
             result.obligations.drain_filter(|projected_obligation| {
                 if !deduped.insert(projected_obligation.clone()) {
                     return true;
                 }
-                // If any global obligations always apply, considering regions, then we don't
-                // need to include them. The `is_global` check rules out inference variables,
-                // so there's no need for the caller of `opt_normalize_projection_type`
-                // to evaluate them.
-                // Note that we do *not* discard obligations that evaluate to
-                // `EvaluatedtoOkModuloRegions`. Evaluating these obligations
-                // inside of a query (e.g. `evaluate_obligation`) can change
-                // the result to `EvaluatedToOkModuloRegions`, while an
-                // `EvaluatedToOk` obligation will never change the result.
-                // See #85360 for more details
-                projected_obligation.is_global(canonical.tcx())
-                    && canonical
-                        .evaluate_root_obligation(projected_obligation)
-                        .map_or(false, |res| res.must_apply_considering_regions())
+                false
             });
 
             if use_cache {