no thir-unsafeck in beta

remove testing via `-Z thir-unsafeck`, since it is not appropriate for beta branch.

Author: pnkfelix

src/test/ui/unsafe/issue-85435-unsafe-op-in-let-under-unsafe-under-closure.rs

@@ -1,6 +1,4 @@
 // check-pass
-// revisions: mir thir
-// [thir]compile-flags: -Z thir-unsafeck
 
 // This is issue #85435. But the real story is reflected in issue #85561, where
 // a bug in the implementation of feature(capture_disjoint_fields) () was