revert using the extension of the blob to determine the syntax highlighting language

nohighlight functionality for a hardcoded set of filenames is kept

app/helpers/blob_helper.rb

 module BlobHelper
   def highlightjs_class(blob_name)
-    if blob_name.include?('.')
-      ext = blob_name.split('.').last
-      return 'language-' + ext
+    if no_highlight_files.include?(blob_name.downcase)
+      'no-highlight'
     else
-      if no_highlight_files.include?(blob_name.downcase)
-        'no-highlight'
-      else
-        blob_name.downcase
-      end
+      blob_name.downcase
     end
   end