Remove keywords from reference because they're already in grammar

Author: mdinger

reference.md

@@ -134,31 +134,6 @@ Tokens are primitive productions in the grammar defined by regular
 production](#string-table-productions) form, and occur in the rest of the
 grammar as double-quoted strings. Other tokens have exact rules given.
 
-### Keywords
-
-<p id="keyword-table-marker"></p>
-
-|          |          |          |          |         |
-|----------|----------|----------|----------|---------|
-| abstract | alignof  | as       | become   | box     |
-| break    | const    | continue | crate    | do      |
-| else     | enum     | extern   | false    | final   |
-| fn       | for      | if       | impl     | in      |
-| let      | loop     | macro    | match    | mod     |
-| move     | mut      | offsetof | override | priv    |
-| proc     | pub      | pure     | ref      | return  |
-| Self     | self     | sizeof   | static   | struct  |
-| super    | trait    | true     | type     | typeof  |
-| unsafe   | unsized  | use      | virtual  | where   |
-| while    | yield    |          |          |         |
-
-
-Each of these keywords has special meaning in its grammar, and all of them are
-excluded from the `ident` rule.
-
-Note that some of these keywords are reserved, and do not currently do
-anything.
-
 ### Literals
 
 A literal is an expression consisting of a single token, rather than a sequence