Revert "Control the fan when it's supposed to be, not when the g-codes are received."

This reverts commit ebdce6c55f0fe90c4907d9935b0d3ec423c18aab.
Revert "Use the software PWM for fan control to not generate annoying sounds. Allow increasing software PWM frequency."

This reverts commit 5bc833d15b745aa9e751417367304d015b1106d3.