expr: Remove nonexistent error UnmatchedClosingBrace

The closing brace without related opening brace is handled literally

src/uu/expr/src/expr.rs

@@ -46,8 +46,6 @@ pub enum ExprError {
     UnmatchedClosingParenthesis,
     #[error("Unmatched \\{{")]
     UnmatchedOpeningBrace,
-    #[error("Unmatched ) or \\}}")]
-    UnmatchedClosingBrace,
     #[error("Invalid content of \\{{\\}}")]
     InvalidBracketContent,
     #[error("Trailing backslash")]

src/uu/expr/src/syntax_tree.rs

@@ -365,9 +365,7 @@ fn check_posix_regex_errors(pattern: &str) -> ExprResult<()> {
             }
             (true, '}') => {
                 if !is_brace_ignored {
-                    escaped_braces = escaped_braces
-                        .saturating_sub(1)
-                        .ok_or(ExprError::UnmatchedClosingBrace)?;
+                    escaped_braces = escaped_braces.saturating_sub(1);
                 }
             }
             _ => {}
@@ -1007,12 +1005,6 @@ mod test {
             Err(ExprError::UnmatchedClosingParenthesis)
         );
 
-        assert_eq!(
-            check_posix_regex_errors(r"abc\}"),
-            Err(ExprError::UnmatchedClosingBrace)
-        );
-    }
-
     #[test]
     fn check_regex_empty_repeating_pattern() {
         assert_eq!(