Open the mdl with notepad and search for "FTP" You'll find two lines (one for the left and one for the right feet) that start with "eventobject" For example:
EventObject "FPTxFBR1" {
ObjectId 78,
EventTrack 1 {
23900,
}
}
EventObject "FPTxFBL1" {
ObjectId 79,
EventTrack 1 {
24233,
}
Select and delete them. IMPORTANT: some parts of a model are identified with an ObjectId number. Deleting the two lines for the footprints you'll leave a gap in their order, so you must renumber everything that is after the lines that you deleted.