Fix checked_conversions lint

Author: nyurik

Cargo.toml

@@ -57,7 +57,6 @@ cast_possible_truncation = "allow"
 cast_possible_wrap = "allow"
 cast_precision_loss = "allow"
 cast_sign_loss = "allow"
-checked_conversions = "allow"
 default_trait_access = "allow"
 explicit_into_iter_loop = "allow"
 flat_map_option = "allow"

bindgen/ir/var.rs

@@ -234,10 +234,7 @@ impl ClangSubItemParser for Var {
                                 assert_eq!(c.len_utf8(), 1);
                                 c as u8
                             }
-                            CChar::Raw(c) => {
-                                assert!(c <= u64::from(u8::MAX));
-                                c as u8
-                            }
+                            CChar::Raw(c) => u8::try_from(c).unwrap(),
                         };
 
                         (TypeKind::Int(IntKind::U8), VarType::Char(c))