rawinput: remove experimental analog features (delay and relative axis mode) (#668)

## Link to GitHub Issue or related Pull Request, if one exists
Related to #181 

## Description of change
This PR removes two features marked as "experimental" for analog axis -
`Delay` and `Relative Axis`.

They have been in spice as experimental option for almost 2 years.. but
they have a fundamental problem of being tied to how often the analog is
polled. Not just how often the game's I/O emulation code polls it, but
literally any source (spice API, overlay, etc).

For `Delay`, the only real usage I'm aware of is for #181 which is
delaying IIDX turntable input. For this, I will follow up with a
separate PR that adds back the delay option specifically for IIDX.

For `Relative Axis` - I'm not quite sure if any one actually uses this.
This could be implemented per-game if some game demands it. Polaris
Chord already has one, for example.

## Testing

src/spice2x/cfg/analog.cpp

@@ -237,8 +237,7 @@ float Analog::applyDeadzone(float raw_value) {
         deadzone = -deadzone;
     }
 
-    // relative mode assumes that user is using a stick, so center is neutral regardless of analog type
-    if (getType() != GameAPI::Analogs::AnalogType::LinearPositive || isRelativeMode()) {
+    if (getType() != GameAPI::Analogs::AnalogType::LinearPositive) {
 
         // calculate values
         const auto delta = value - 0.5f;