Remove Section on non-idempotent memory handling

[christian-herber-nxp]

from @ved-rivos:

Section 2.6

"Software should only use these instructions on non-idempotent memory regions when software can tolerate the required memory accesses being issued repeatedly in the case that they cause exceptions." This text is a bit misleading as the region cannot be non-idempotent if repeated accesses can be tolerated. That said this whole section can be deleted as the allowance of redoing the memory access has been discussed in earlier sections at length and this property is not different than the existing FLD/FSD for RV32.