Accessibility: Remove meaningless alt text.

It just gets in the way of screen readers.

r2/r2/templates/captcha.html

@@ -36,7 +36,7 @@ ${rounded_captcha()}
   <input name="iden" value="${iden}" type="hidden"/>
 
   <img class="capimage"
-       alt="i wonder if these things even work" 
+       alt="visual CAPTCHA"
        %if hasattr(thing, "iden"):
        src="/captcha/${thing.iden}.png" 
        %else:

r2/r2/templates/errorpage.html

@@ -26,7 +26,7 @@ from r2.lib.filters import unsafe, safemarkdown
 %>
 
 <div id="classy-error" class="content">
-  <img src="${static(thing.image_url)}" alt="an unhappy alien" />
+  <img src="${static(thing.image_url)}" alt="" />
 
   <h1>${thing.title}</h1>
   <div class="errorpage-message">

r2/r2/templates/over18.html

@@ -26,7 +26,7 @@
   <p class="error">
     ${_("you must be at least eighteen to view this reddit")}
   </p>
-  <img src="${static('over18.png')}" alt="jedberg alien" />
+  <img src="${static('over18.png')}" alt="" />
   
   <form method="post" action="" class="pretty-form"
       ${"target='_top'" if c.cname else ""}>

r2/r2/templates/passwordverificationform.html

@@ -28,7 +28,7 @@
 <%namespace file="utils.html" import="error_field"/>
 
 <div class="content over18" style="text-align: center">
-  <img src="${static('over18.png')}" alt="jedberg alien" />
+  <img src="${static('over18.png')}" alt="" />
 
   <h1>let me see your papers</h1>