TouchInputMapper: remove gestureMode parameter

This was being set from an evdev property and potentially from IDC
files. It seems that at some point [0] it affected the way pointers were
drawn for touchpads in the old stack, but it's no longer used.

[0]: the farthest back I was able to easily trace this field in the code
     history was to change I5f571fe86eb570885ae994e1f0552fb558930346

Test: $ atest --host inputflinger_tests
Flag: EXEMPT refactor
Bug: 245989146
Change-Id: I1538c0c6f23f33a27e346f6cbc0e1181d5beb005