Remove unused META_CONFIG_PREFIX

This variable was never actually used. I suppose I've been adding it for
places where the config should be added as a prefix. However, this would be
inconsistent and now would also mean a confusing overlap with the
namespacing feature. So let's just remove it.

Author: Martchus

cmake/modules/BasicConfig.cmake

@@ -52,7 +52,6 @@ else ()
     set(META_CONFIG_NAME "${CONFIGURATION_NAME}")
 endif ()
 if (META_CONFIG_NAME)
-    set(META_CONFIG_PREFIX "${META_CONFIG_NAME}-")
     set(META_CONFIG_SUFFIX "-${META_CONFIG_NAME}")
 endif ()
 if (CONFIGURATION_DISPLAY_NAME)