cmake: Remove prefix suppression for scripting plugins.

SWIG uses the prefix target property to prefix generated Python
libraries with an underscore (so that obspython.py is loaded first,
which acts as a shim for the actual _obspython.pyd library on Windows).

Usually the prefix is set to an empty string on Windows (to avoid the
automatic "lib" prefix used by CMake), but this also removed the
necessary underscore prefix required for the Python library.

cmake/Modules/ObsHelpers.cmake

@@ -102,8 +102,6 @@ endfunction()
 
 # Helper function to set up OBS scripting plugin targets
 function(setup_script_plugin_target target)
-  set_target_properties(${target} PROPERTIES PREFIX "")
-
   install(
     TARGETS ${target}
     LIBRARY DESTINATION ${OBS_SCRIPT_PLUGIN_DESTINATION}