fam_wrappers: Remove code snippet of kvm_save2.len

Code snippet for len field of kvm_xsave2 is outdate for a long while,
which also fails to compile. Change the code snippet to pseudo code.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

Author: RuoqingHe

kvm-bindings/src/x86_64/fam_wrappers.rs

@@ -132,12 +132,10 @@ pub type MsrList = FamStructWrapper<kvm_msr_list>;
 pub struct kvm_xsave2 {
     /// The length, in units of sizeof::<__u32>(), of the FAM in [`kvm_xsave`].
     ///
-    /// Note that `KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)` returns the size of the entire
-    /// `kvm_xsave` structure, e.g. the sum of header and FAM. Thus, this `len` field
-    /// is equal to
-    /// ```norun
-    /// (KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) - sizeof::<kvm_xsave>()).div_ceil(sizeof::<__u32>())
-    /// ```
+    /// Note that `KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)` returns the size of the
+    /// entire `kvm_xsave` structure, e.g. the sum of header and FAM. Thus, this
+    /// `len` field is equal to
+    /// `(KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) - sizeof::<kvm_xsave>()).div_ceil(sizeof::<__u32>()`.
     pub len: usize,
     pub xsave: kvm_xsave,
 }