Remove margin from pre in code.scss since it's already set in reboot (twbs#24366)

Author: andresgalante

scss/_code.scss

@@ -42,8 +42,6 @@ kbd {
 // Blocks of code
 pre {
   display: block;
-  margin-top: 0;
-  margin-bottom: 1rem;
   font-size: $code-font-size;
   color: $pre-color;