content: Remove right margin for event-content

This was originally introduced at fc02302620 to match mockups, but
seems to be better without.

Also adjust the CSS selector below to have them matching on RTL.

data/resources/style.css

@@ -357,13 +357,14 @@ login {
   margin-top: 6px;
 }
 
-.room-history .event-content {
-  margin-right: 46px;
+.room-history row:not(.has-header) .event-content:dir(ltr),
+.room-history row:not(.has-header) message-reactions:dir(ltr) {
+  margin-left: 46px;
 }
 
-.room-history row:not(.has-header) .event-content,
-.room-history row:not(.has-header) message-reactions {
-  margin-left: 46px;
+.room-history row:not(.has-header) .event-content:dir(rtl),
+.room-history row:not(.has-header) message-reactions:dir(rtl) {
+  margin-right: 46px;
 }
 
 .room-history .event-content .emoji {