Fix paths rbc-run uses to access the rbc tools.

This was broken in aosp/1878498; ccross@ submitted aosp/1875758 between
writing that change and submitting it, which changed the paths to mk2rbc
and rbcrun, thereby breaking Starlark product configuration.

Test: Presubmits.
Change-Id: I185489589997e6bdc815a54a8f6f328c18f813d0
diff --git a/scripts/rbc-run b/scripts/rbc-run
index 9d30199..ecc6edd 100755
--- a/scripts/rbc-run
+++ b/scripts/rbc-run
@@ -5,25 +5,12 @@
 [[ $# -gt 0 && -f "$1" ]] || { echo "Usage: ${0##*/} product.mk [Additional rbcrun arguments]" >&2; exit 1; }
 set -eu
 
-case $(uname -s) in
-  Linux)
-    declare -r os="linux-x86";
-    ;;
-  Darwin)
-    declare -r os="darwin-x86";
-    ;;
-  *)
-    echo "Unknown OS: $(uname -s)" >&2;
-    exit 1;
-    ;;
-esac
-
 declare -r output_root="${OUT_DIR:-out}"
-declare -r runner="${output_root}/soong/host/${os}/bin/rbcrun"
-declare -r converter="${output_root}/soong/host/${os}/bin/mk2rbc"
-declare -r launcher="$output_root/launchers/run.rbc"
+declare -r runner="${output_root}/soong/rbcrun"
+declare -r converter="${output_root}/soong/mk2rbc"
+declare -r launcher="${output_root}/launchers/run.rbc"
 declare -r makefile="$1"
 shift
-"$converter" -mode=write -r --outdir "$output_root" --launcher="$launcher" "$makefile"
-"$runner" RBC_OUT="make,global" RBC_DEBUG="${RBC_DEBUG:-}" $@ "$launcher"
+"${converter}" -mode=write -r --outdir "${output_root}" --launcher="${launcher}" "${makefile}"
+"${runner}" RBC_OUT="make,global" RBC_DEBUG="${RBC_DEBUG:-}" $@ "${launcher}"