Meta: Remove an outdated `MAKE_DIRECTORY` call for pnp IDs

We are downloading these directly into the build directory now, and
generating the source code from there, so we no longer need the
manually created directory.

While we are at it, remove two variables that seem to be no longer in
use, and at least one of which is confusing regarding a missing prefix.

Meta/CMake/pnp_ids.cmake

@@ -1,12 +1,9 @@
 include(${CMAKE_CURRENT_LIST_DIR}/utils.cmake)
 
-set(PNP_IDS_FILE pnp.ids)
 set(PNP_IDS_URL http://www.uefi.org/uefi-pnp-export)
 set(PNP_IDS_EXPORT_PATH ${CMAKE_BINARY_DIR}/pnp_ids.html)
-set(PNP_IDS_INSTALL_PATH ${CMAKE_INSTALL_DATAROOTDIR}/${PNP_IDS_FILE})
 
 if (ENABLE_PNP_IDS_DOWNLOAD)
-    file(MAKE_DIRECTORY ${CMAKE_INSTALL_DATAROOTDIR})
     download_file("${PNP_IDS_URL}" "${PNP_IDS_EXPORT_PATH}")
 
     set(PNP_IDS_HEADER PnpIDs.h)