don't explicitly require 'external: 'body

this breaks propagate_type_outlives

Author: lcnr

compiler/rustc_borrowck/src/type_check/opaque_types.rs

@@ -73,10 +73,6 @@ pub(super) fn force_regions_to_existential_externals<'tcx>(
                     ConstraintCategory::OpaqueType,
                     typeck.constraints,
                 );
-                constraint_conversion.convert(
-                    ty::OutlivesPredicate(external_reg.into(), fr_fn_body),
-                    ConstraintCategory::OpaqueType,
-                );
                 constraint_conversion.convert(
                     ty::OutlivesPredicate(external_reg.into(), r),
                     ConstraintCategory::OpaqueType,