reference: String is not an instantiation of the str type

Author: Ulrik Sverdrup

src/doc/reference.md

@@ -3427,7 +3427,7 @@ UTF-32 string.
 A value of type `str` is a Unicode string, represented as an array of 8-bit
 unsigned bytes holding a sequence of UTF-8 codepoints. Since `str` is of
 unknown size, it is not a _first-class_ type, but can only be instantiated
-through a pointer type, such as `&str` or `String`.
+through a pointer type, such as `&str`.
 
 ### Tuple types