Remove redundant CSRF explanation and note deprecation
Remove redundant CSRF explanation and note deprecation

Aaron1992/wtforms,pawl/wtforms,Aaron1992/wtforms,jmagnusson/wtforms,wtforms/wtforms,subyraman/wtforms,hsum/wtforms,skytreader/wtforms,Xender/wtforms,cklein/wtforms,pawl/wtforms,crast/wtforms