syntax: drop some Result type aliases

I'm overall coming around to the opinion that these tend to make the
code harder to read. So I've been steadily dropping the Result aliases.

regex-syntax/src/ast/parse.rs

@@ -171,7 +171,7 @@ impl ParserBuilder {
     /// constant stack space and moving the call stack to the heap), other
     /// crates may.
     ///
-    /// This limit is not checked until the entire Ast is parsed. Therefore,
+    /// This limit is not checked until the entire AST is parsed. Therefore,
     /// if callers want to put a limit on the amount of heap space used, then
     /// they should impose a limit on the length, in bytes, of the concrete
     /// pattern string. In particular, this is viable since this parser

regex-syntax/src/hir/translate.rs

@@ -1058,7 +1058,7 @@ impl<'t, 'p> TranslatorI<'t, 'p> {
     fn convert_unicode_class_error(
         &self,
         span: &Span,
-        result: unicode::Result<hir::ClassUnicode>,
+        result: core::result::Result<hir::ClassUnicode, unicode::Error>,
     ) -> Result<hir::ClassUnicode> {
         result.map_err(|err| {
             let sp = span.clone();