Can I remove excess damp proof membrane under garage concrete floor?
If the garage isn't below grade, doesn't have a sump pump on its level, there's no drain pipe open to daylight out in the yard and you don't have holes drilled at the base of the walls. Then yes, you can cut it down, as it's just newer concrete of this century that normally requires a water and vapor barrier...typically it's clear or black 6-mil polyvinyl sheeting required by code.

If yours were a very minor part of a proper drying or water handling system it would be hard and stiff plastic that's bubbled or ridged, like the picture below.