Can't build for Mac or Linux when OpenVR XR is in project

[mastayb]

There are two copies of libopenvr_api.so colliding with each other, preventing macOS and Linux builds.

Tested in Unity 2020.3.7f1, 2020.1.7f1, and 2019.4.12f1 with the same results, using the openvr-1.1.4 bundled in the SteamVR plugin and installed from source.

BuildPlayer: start building target 2
- Starting script compilation
[...]
- Finished script compilation in 8.253391 seconds
Plugin 'libopenvr_api.so' is used from several locations:
 Packages/com.valvesoftware.unity.openvr/Runtime/x64/lib/x64/libopenvr_api.so would be copied to <PluginPath>/libopenvr_api.so
 Packages/com.valvesoftware.unity.openvr/Runtime/x64/libopenvr_api.so would be copied to <PluginPath>/libopenvr_api.so
Please fix plugin settings and try again.

UnityEngine.DebugLogHandler:Internal_Log(LogType, LogOption, String, Object)
[...]
/Users/builduser/buildslave/unity/build/Editor/Mono/BuildPlayerWindow.cs:136)
 
(Filename: /Users/builduser/buildslave/unity/build/Editor/Mono/Modules/DefaultPluginImporterExtension.cs Line: 218)

Plugins colliding with each other.```