Revert "feature: allow dot on username"

This reverts commit 22400b6b

src/views/partials/widgets/orbit-username-field.pug

@@ -2,4 +2,4 @@ if componentSet.has('admin') && componentSet.has('chat')
   solid-widget(name='orbit-username-field')
     template
       label ${label}
-      input(type="text" title='' pattern="[a-zA-Z0-9\.]+" label="${label}" data-trans='title=user.create.labelUsernameTitle' name="username" required value="\${value}" data-holder)
+      input(type="text" title='' pattern="[a-zA-Z0-9]+" label="${label}" data-trans='title=user.create.labelUsernameTitle' name="username" required value="\${value}" data-holder)
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