Fix svg colors in file list table (#17903)

* Fix svg colors in file list table

Turns out this can be fixed by just removing rules. Directory and file
icons have other rules that still make them color correctly.

* tweak color on file icons

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/less/_repository.less

@@ -304,7 +304,6 @@
         .svg {
           margin-left: 3px;
           margin-right: 5px;
-          color: #777777;
 
           &.octicon-reply {
             margin-right: 10px;
@@ -314,6 +313,11 @@
           &.octicon-file-submodule {
             color: var(--color-primary);
           }
+
+          &.octicon-file,
+          &.octicon-file-symlink-file {
+            color: var(--color-secondary-dark-7);
+          }
         }
       }