Remove copy of current const prop tests and add a few new tests

src/test/mir-opt/dataflow-const-prop/inherit_overflow.rs

@@ -0,0 +1,8 @@
+// compile-flags: -Coverflow-checks=off -Zunsound-mir-opts
+
+// EMIT_MIR inherit_overflow.main.DataflowConstProp.diff
+fn main() {
+    // After inlining, this will contain a `CheckedBinaryOp`. The overflow
+    // must be ignored by the constant propagation to avoid triggering a panic.
+    let _ = <u8 as std::ops::Add>::add(255, 1);
+}