🔥 refactor: remove useless code

An image border was set in _image.scss and unset in main.scss.

sass/main.scss

@@ -166,10 +166,6 @@ p {
   font-size: 1.2em;
 }
 
-img {
-  border: none;
-}
-
 @media only screen and (max-width: 1000px) {
   .content {
     max-width: var(--normal-layout-width);

sass/parts/_image.scss

@@ -1,8 +1,3 @@
-img {
-  border: 3px solid #ececec;
-  max-width: 100%;
-}
-
 figure {
   box-sizing: border-box;
   display: inline-block;