Acquisition bug: don't collect at 4 kHz

With the current version of the CTF MEG acquisition software (Acq v 6.1) which we’ve been using since changing acquisition computer in 2019, some data samples are not recorded if the sampling rate is set to 4 kHz, possibly 1 sample every 33 ms. This is true for all channels, and prevents continuous head localization (CHL) from working properly. I don’t believe any recent studies used this, but wanted to advertise it to avoid potential issues and to not forget it.