Remove bottom from the reference

Fixes rust-lang#20172

Author: steveklabnik

src/doc/reference.md

@@ -1253,9 +1253,7 @@ fn my_err(s: &str) -> ! {
 We call such functions "diverging" because they never return a value to the
 caller. Every control path in a diverging function must end with a `panic!()` or
 a call to another diverging function on every control path. The `!` annotation
-does *not* denote a type. Rather, the result type of a diverging function is a
-special type called ⊥ ("bottom") that unifies with any type. Rust has no
-syntax for ⊥.
+does *not* denote a type.
 
 It might be necessary to declare a diverging function because as mentioned
 previously, the typechecker checks that every control path in a function ends