Revert anon namespace in fft/main
Revert anon namespace in fft/main

Added to prevent duplicate symbol error on Bazel+MSVC, now causing
ambiguous symbol. Reverting for now, will fix another way for the case
in question.

kgnk/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,psuriana/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,psuriana/Halide,kgnk/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,kgnk/Halide