remove invalid alt tag

Author: JPrevost

app/views/layouts/_libraries_footer.html.erb

@@ -3,7 +3,7 @@
     <div class="footer-main" aria-label="MIT Libraries footer">
       <div class="identity">
         <div class="wrap-logo-lib">
-          <a href="https://libraries.mit.edu" class="logo-mit-lib" alt="MIT Libraries Logo">
+          <a href="https://libraries.mit.edu" class="logo-mit-lib">
               <span class="sr">MIT Libraries home</span>
               <img
                 src="https://cdn.libraries.mit.edu/files/branding/local/mitlib-wordmark.svg"