Link to the keyword family page from the field types docs. (#61819)

We now link to the top-level keyword type family page instead of its individual
subsections. This better fits the page format, where each type name is a link.

docs/reference/mapping/types.asciidoc

@@ -23,9 +23,8 @@ type: `boolean`.
 
 <<binary,`binary`>>::   Binary value encoded as a Base64 string.
 <<boolean,`boolean`>>:: `true` and `false` values.
-Keyword::               The keyword family, including <<keyword, `keyword`>>,
-                        <<constant-keyword-field-type,`constant_keyword`>>, and
-                        <<wildcard-field-type, `wildcard`>>.
+<<keyword, Keywords>>:: The keyword family, including `keyword`, `constant_keyword`,
+                        and `wildcard`.
 <<number,Numbers>>::    Numeric types, such as `long` and `double`, used to
                         express amounts.
 Dates::                 Date types, including <<date,`date`>> and