clean up error codeS E0229 and E0261

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0229.md

@@ -1,5 +1,7 @@
 An associated type binding was done outside of the type parameter declaration
-and `where` clause. Erroneous code example:
+and `where` clause.
+
+Erroneous code example:
 
 ```compile_fail,E0229
 pub trait Foo {

src/librustc_error_codes/error_codes/E0261.md

@@ -1,7 +1,6 @@
-When using a lifetime like `'a` in a type, it must be declared before being
-used.
+An undeclared lifetime was used.
 
-These two examples illustrate the problem:
+Erroneous code example:
 
 ```compile_fail,E0261
 // error, use of undeclared lifetime name `'a`