Clarify and correct comment about multi_byte_tokens

crates/ra_syntax/src/grammar.ron

@@ -25,9 +25,9 @@ Grammar(
         ["^", "CARET"],
         ["%", "PERCENT"],
     ],
-    // TODO: Confirm surmision: the tokens which cannot be recorded in a single UTF-8 byte
+    // Tokens for which the longest match must be chosen (e.g. `..` is a DOTDOT, but `.` is a DOT)
     multi_byte_tokens: [
-        [".", "DOT"], // Note: DOT is here because <TODO: REASON>
+        [".", "DOT"],
         ["..", "DOTDOT"],
         ["...", "DOTDOTDOT"],
         ["..=", "DOTDOTEQ"],