bpo-38835: Don't use PyFPE_START_PROTECT and PyFPE_END_PROTECT (GH-17231)

The PyFPE_START_PROTECT() and PyFPE_END_PROTECT() macros are empty:
they have been doing nothing for the last year  (since commit
735ae8d139a673b30b321dc10acfd3d14f0d633b), so stop using them.