Remove ICM Gyro Pre-filter

[andyp1per]

This PR is on top of #14423 and removes the gyro pre-filter that is applied in the ICM drivers.
There are a few reasons for doing this:

• You only want as much filtering as you need and what you need will vary. A fixed 188Hz filter removes that configurability.
• With the introduction of INS_GYRO_RATE we have remove the fixed backend rate of 1000Hz, a fixed 188Hz is likely to affect the gyro values differently as we modify the backend rate
• It introduces delay (and CPU cost)
• With notch filtering its now likely less important
• It makes it harder for the FFT to track noise.

So although removing the filter will inevitably add some noise. The question is - does it matter?

I ran tests with a gyro rate of 2kHz on an MPU6000 with/without and with double-notches. I picked 2kHz here because this was the frequency at which the differences were most evident. These were the results:

Standard:

No pre-filter:

No pre-filter, double notches:

A few things to note:

• There is more noise without the filter
• The noise peaks are much clearer
• The noise levels are perfectly acceptable
• Double-notches squash the extra noise very nicely
• There is no discernable aliasing noise

Note to reviewers - this is actually a two-line change, most of the changes are in #14423

[lthall]

This is one of those PR's where we need a good reason not to do it.

I suspect that this was supposed to be removed a long time ago but was overlooked.

[proficnc]

I agree, unless a valid reason for keeping this filter is found, it should be removed.

[peterbarker]

Please tweak the commit message; you're not just "disabling" it, you're nuking it completely :-) The PR title is correct...

Any idea why there were different filter constants for the v2 sensor?

This was done.