Remove unnecessary ProductTypes and std::decay in FEValues functions
Remove unnecessary ProductTypes and std::decay in FEValues functions

With the current functionality my application of these two features in
the FEValues function is now overly defensive. So this effectively
reverts some of the changes made in #4951, as #4893 makes some use of
ProductType unnecessary and #5251 ensures compatible conversions between
numbers of all CV qualifications.
sairajat/dealii,naliboff/dealii,sairajat/dealii,sairajat/dealii,sairajat/dealii,sairajat/dealii,naliboff/dealii,sairajat/dealii,naliboff/dealii,naliboff/dealii,naliboff/dealii,naliboff/dealii,naliboff/dealii,sairajat/dealii