Deprecate the header fassign.hh

See FS1508. C++11 initializer lists should be used instead.
Remove the {fvector,fmatrix}_assigner from the tests

These classes are deprecated, and some of the tests cause
problems with ctest due to a destructor throwing an exception.
It seems easier to remove the tests directly, as the tested code
is deprecated anyway.
Adjust fmatrixtest to use initializer lists.
Also remove testfconstruct.cc and all associated tests