Remove code-view class from diff view (#13011)

code-view class seems unecessary here as everything needed style wise comes from various diff classes. This allows comments and comment editor to be styled properly and fixes linked bug.

Fixes #13010

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

web_src/less/_base.less

@@ -997,6 +997,7 @@ i.icon.centerlock {
   color: rgba(27, 31, 35, .3);
   width: 1%;
   user-select: none;
+  font-family: @monospaced-fonts, monospace;
 
   span {
     &.bottom-line {