[prim] remove FPV related assertions
[prim] remove FPV related assertions

prim_packer.sv has FPV related assumptions that limits the input data.
As prim_packer uses in other modules, these assumptions should be placed
outside of the module itself but placed in _fpv testbench. Those
assumptions are removed.

Signed-off-by: Eunchan Kim <cb7bc7ceb22698f298c67faa994fd9ddf3cab298@opentitan.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan