vulkan-validation-layers: cleanup recipe

Commit doesn't change build behavior

* Removes ${libdir} from FILES:${PN} as its not required.
* Updates PACKAGECONFIG to uses just one @bb.utils.filter call.
* Updates GLSLANG_INSTALL_DIR to <recipe-sysroot>/lib${64} as
  that contains the actual directory of the glslang .cmake
  config files.

Signed-off-by: Vincent Davis Jr <vince@underview.tech>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>