Don't show the upload option if max_attachment_size_kb is 0.

app/assets/javascripts/discourse/controllers/upload_selector_controller.js

@@ -8,8 +8,12 @@
   @module Discourse
 **/
 Discourse.UploadSelectorController = Discourse.Controller.extend(Discourse.ModalFunctionality, {
-  local: true,
-  remote: Em.computed.not("local"),
+  local: Em.computed.not("remote"),
+  remote: Em.computed.not("allowLocal"),
+
+  allowLocal: function() {
+    return Discourse.SiteSettings.max_attachment_size_kb > 0;
+  }.property(),
 
   actions: {
     useLocal: function() { this.set("local", true); },

app/assets/javascripts/discourse/templates/modal/upload_selector.js.handlebars

@@ -1,4 +1,5 @@
 <div class="modal-body">
+  {{#if allowLocal}}
     <div class="radios">
       <input type="radio" id="local" value="local" name="upload" {{action useLocal}}>
       <label class="radio" for="local">{{i18n upload_selector.from_my_computer}}</label>
@@ -9,6 +10,7 @@
         </div>
       {{/if}}
     </div>
+  {{/if}}
   <div class="radios">
     <input type="radio" id="remote" value="remote" name="upload" {{action useRemote}}>
     <label class="radio" for="remote">{{i18n upload_selector.from_the_web}}</label>