Remove no longer used contract_checks intrinsic

The contract_checks compiler flag is now used to determine
if runtime contract checks should be enabled, as opposed
to the compiler intrinsic as previously.

Author: dawidl022

core/src/intrinsics/mod.rs

@@ -2631,24 +2631,6 @@ pub const unsafe fn const_make_global(ptr: *mut u8) -> *const u8 {
     ptr
 }
 
-/// Returns whether we should perform contract-checking at runtime.
-///
-/// This is meant to be similar to the ub_checks intrinsic, in terms
-/// of not prematurely committing at compile-time to whether contract
-/// checking is turned on, so that we can specify contracts in libstd
-/// and let an end user opt into turning them on.
-#[unstable(feature = "contracts_internals", issue = "128044" /* compiler-team#759 */)]
-#[rustc_const_unstable(feature = "contracts", issue = "128044")]
-#[inline(always)]
-#[lang = "contract_checks"]
-#[rustc_intrinsic]
-pub const fn contract_checks() -> bool {
-    // FIXME: should this be `false` or `cfg!(contract_checks)`?
-
-    // cfg!(contract_checks)
-    false
-}
-
 /// Check if the pre-condition `cond` has been met.
 ///
 /// By default, if `contract_checks` is enabled, this will panic with no unwind if the condition