Rollup merge of #67837 - GuillaumeGomez:clean-up-err-codes, r=Dylan-DPC

Clean up err codes

r? @Dylan-DPC

src/librustc_error_codes/error_codes/E0136.md

-A binary can only have one entry point, and by default that entry point is the
-function `main()`. If there are multiple such functions, please rename one.
+More than one `main` function was found.
 
 Erroneous code example:
 
@@ -14,3 +13,7 @@ fn main() { // error!
     // ...
 }
 ```
+
+A binary can only have one entry point, and by default that entry point is the
+`main()` function. If there are multiple instances of this function, please
+rename one of them.

src/librustc_error_codes/error_codes/E0161.md

-A value was moved. However, its size was not known at compile time, and only
-values of a known size can be moved.
+A value was moved whose size was not known at compile time.
 
 Erroneous code example:
 

src/librustc_error_codes/error_codes/E0164.md

-This error means that an attempt was made to match a struct type enum
-variant as a non-struct type:
+Something which is neither a tuple struct nor a tuple variant was used as a
+pattern.
+
+Erroneous code example:
 
 ```compile_fail,E0164
-enum Foo { B { i: u32 } }
+enum A {
+    B,
+    C,
+}
+
+impl A {
+    fn new() {}
+}
 
-fn bar(foo: Foo) -> u32 {
+fn bar(foo: A) {
     match foo {
-        Foo::B(i) => i, // error E0164
+        A::new() => (), // error!
+        _ => {}
     }
 }
 ```
 
-Try using `{}` instead:
+This error means that an attempt was made to match something which is neither a
+tuple struct nor a tuple variant. Only these two elements are allowed as a
+pattern:
 
 ```
-enum Foo { B { i: u32 } }
+enum A {
+    B,
+    C,
+}
+
+impl A {
+    fn new() {}
+}
 
-fn bar(foo: Foo) -> u32 {
+fn bar(foo: A) {
     match foo {
-        Foo::B{i} => i,
+        A::B => (), // ok!
+        _ => {}
     }
 }
 ```