Fixes in transforms.py

[benglewis]

Change docstring which uses '\w' to add r before string to make it a "raw string" and thus prevent it from raising Python errors. Fix typing of BaseRemoveTransform

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.