input-forms.xml: Run through tidy

Standardize indentation and remove unneccessary white spaces using
tidy:

    tidy -xml -iq -m config/input-forms.xml

xmllint works too, but it reduces empty tags like <required></required>
to <required/>, which isn't as readable and could be confusing if
you go to modify the input forms and aren't someone who stares at
XML all day.