MD Settings cleanup: Remove unused paper-icon-item CSS rule.

BUG=None
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2892323002
Cr-Commit-Position: refs/heads/master@{#473416}

chrome/browser/resources/settings/settings_shared_css.html

@@ -206,10 +206,6 @@
         opacity: var(--settings-disabled-opacity);
       }
 
-      .list-item > paper-icon-item {
-        padding: 0;
-      }
-
       /* This button has no ink ripple. */
       .list-button[is='action-link'] {
         align-items: center;