The XR Legacy Input Helpers package results in errors that prevent builds occurring.

Reproduction Steps:
1. Open the attached project, targeting a platform that doesn't support XR
2. Observe the errors:
Library\PackageCache\com.unity.xr.legacyinputhelpers@1.3.7\Runtime\TrackedPoseDriver\TrackedPoseDriver.cs(352,16): error CS0246: The type or namespace name 'BasePoseProvider' could not be found (are you missing a using directive or an assembly reference?)
Library\PackageCache\com.unity.xr.legacyinputhelpers@1.3.7\Runtime\TrackedPoseDriver\TrackedPoseDriver.cs(344,9): error CS0246: The type or namespace name 'BasePoseProvider' could not be found (are you missing a using directive or an assembly reference?)