Remove selection border from change-list

Border appears underneath table header due to the table having
border-collapse set. Needs more thought, and can be left out in the
meantime.

Change-Id: I9a25601fba6aafd37148e8de971360905b595200
diff --git a/polygerrit-ui/app/styles/app-theme.html b/polygerrit-ui/app/styles/app-theme.html
index 354f223..5888f92 100644
--- a/polygerrit-ui/app/styles/app-theme.html
+++ b/polygerrit-ui/app/styles/app-theme.html
@@ -27,7 +27,6 @@
 
   /* Following are not part of plugin API. */
   --selection-background-color: #f1f5fb;
-  --selection-border-color: #cadcfa;
   --view-background-color: #fff;
   --default-horizontal-margin: 1rem;
   --font-family: 'Roboto', -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol';
diff --git a/polygerrit-ui/app/styles/gr-change-list-styles.html b/polygerrit-ui/app/styles/gr-change-list-styles.html
index c7d9691..497b5e4 100644
--- a/polygerrit-ui/app/styles/gr-change-list-styles.html
+++ b/polygerrit-ui/app/styles/gr-change-list-styles.html
@@ -27,7 +27,6 @@
       gr-change-list-item[selected],
       gr-change-list-item:focus {
         background-color: var(--selection-background-color);
-        border: 1px solid var(--selection-border-color);
       }
       .topHeader ~ gr-change-list-item:first-of-type,
       .topHeader + .groupHeader {