No need for a zst constructor method when we can have a constant

compiler/rustc_middle/src/mir/interpret/value.rs

@@ -180,7 +180,7 @@ impl<'tcx, Tag> Scalar<Tag> {
 
     #[inline]
     pub fn zst() -> Self {
-        Scalar::Int(ScalarInt::zst())
+        Scalar::Int(ScalarInt::ZST)
     }
 
     #[inline(always)]

compiler/rustc_middle/src/ty/consts/int.rs

@@ -183,11 +183,6 @@ impl ScalarInt {
         );
     }
 
-    #[inline]
-    pub fn zst() -> Self {
-        Self::null(Size::ZERO)
-    }
-
     #[inline]
     pub fn null(size: Size) -> Self {
         Self { data: 0, size: size.bytes() as u8 }