configure: Remove SUPPORTED_TARGET support

This is not used any more

Author: alexcrichton

configure

@@ -912,10 +912,6 @@ CFG_MANDIR=${CFG_MANDIR%/}
 CFG_DOCDIR=${CFG_DOCDIR%/}
 CFG_HOST="$(echo $CFG_HOST | tr ',' ' ')"
 CFG_TARGET="$(echo $CFG_TARGET | tr ',' ' ')"
-CFG_SUPPORTED_TARGET=""
-for target_file in ${CFG_SRC_DIR}mk/cfg/*.mk; do
-  CFG_SUPPORTED_TARGET="${CFG_SUPPORTED_TARGET} $(basename "$target_file" .mk)"
-done
 
 # copy build-triples to host-triples so that builds are a subset of hosts
 V_TEMP=""