Revert "Add support for floating-point option `ffp-eval-method` and for"

This reverts commit 32b73bc6.

This breaks builds on macOS in some configurations, because
__FLT_EVAL_METHOD__ is set to an unexpected value.

E.g.
https://green.lab.llvm.org/green/job/clang-stage1-RA/28282/consoleFull#129538464349ba4694-19c4-4d7e-bec5-911270d8a58c

More details available in the review thread
https://reviews.llvm.org/D109239