Remove UTF8 checkmark from homepage search

Rails adds utf8='checkmark' to form posts (also if method is GET). This is for IE5-8. See more: http://stackoverflow.com/questions/3222013/what-is-the-snowman-param-in-ruby-on-rails-3-forms-for/3348524#3348524

However, this breaks BingBot (https://sharetribe.airbrake.io/projects/15448/groups/1157264204336826281)

**Solution:** Remove the utf8 checkmark from homepage search by not using default form helper.