Revert "Add error explanation for E00070"

This reverts commit 25037c9.

Author: GuillaumeGomez

src/librustc_typeck/diagnostics.rs

@@ -170,30 +170,6 @@ Since `return;` is just like `return ();`, there is a mismatch between the
 function's return type and the value being returned.
 "##,
 
-E0070: r##"
-You tried to change the value of a const variable, which is not possible. Bad
-example:
-
-```
-const SOME_CONST : i32 = 12;
-
-fn some_function() {
-    SOME_CONST = 14; // error !
-}
-```
-
-Constant variables' value can be changed once it has been set. Please take a
-look to static keyword if you want something similar but mutable:
-
-```
-static mut SOME_NOT_CONST : i32 = 12;
-
-fn some_function() {
-    SOME_NOT_CONST = 14; // that's good !
-}
-```
-"##,
-
 E0081: r##"
 Enum discriminants are used to differentiate enum variants stored in memory.
 This error indicates that the same value was used for two or more variants,
@@ -682,6 +658,7 @@ register_diagnostics! {
     E0060,
     E0061,
     E0068,
+    E0070,
     E0071,
     E0072,
     E0073,