simplify similar_tokens from Option<Vec<_>> to Vec<_>

compiler/rustc_parse/src/parser/expr.rs

@@ -3115,8 +3115,7 @@ impl<'a> Parser<'a> {
             let arm_body;
             let is_fat_arrow = this.check(exp!(FatArrow));
             let is_almost_fat_arrow = TokenKind::FatArrow
-                .similar_tokens()
-                .is_some_and(|similar_tokens| similar_tokens.contains(&this.token.kind));
+                .similar_tokens().contains(&this.token.kind);
 
             // this avoids the compiler saying that a `,` or `}` was expected even though
             // the pattern isn't a never pattern (and thus an arm body is required)