Simplify code

[AlanGriffiths]

Many years ago we tried to get some libinput_event_touch_ functions upstreamed to libinput, but they were rejected. Ubuntu no longer carries the patch that implements them.

There are simpler ways to do what this code did (e.g. resolve the possible library functions at compile time or make the function pointers global) but, as the functions are never available, it doesn't need to do it anyway.

The new version will give a compile error if the functions are introduced into libinput and we can fix the code appropriately if that happens.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (bc6864b) 77.86% compared to head (719e71c) 77.86%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3174      +/-   ##
==========================================
- Coverage   77.86%   77.86%   -0.01%     
==========================================
  Files        1070     1080      +10     
  Lines       74917    75341     +424     
==========================================
+ Hits        58334    58664     +330     
- Misses      16583    16677      +94     

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[RAOF]

Huh, I was sure I'd reviewed this before!

Yeah, this code was weird when I looked at it recently, too 😁