Explain using the just-built file program during build

Also drop echoing the parameter line, that was for debugging only.

debian/rules

@@ -5,6 +5,8 @@ export DEB_BUILD_MAINT_OPTIONS = hardening=+all
 # HOWMANY is the number of bytes looked at by file
 CFLAGS += -DHOWMANY=0x18000
 
+# Unless cross-building, use the just-built file binary in the various
+# debhelper programs. See #948619
 ifeq ($(DEB_BUILD_ARCH),$(DEB_HOST_ARCH))
 	export PATH := $(CURDIR)/debian/run-file:$(PATH)
 	export CURDIR

debian/run-file/file

@@ -6,8 +6,6 @@ REGULAR_FILE=/usr/bin/file
 BUILT_FILE="$CURDIR/debian/tmp/usr/bin/file"
 
 if [ -x "$BUILT_FILE" ] ; then
-    echo "Running just-built file, args: $@" >&2
-
     export LD_LIBRARY_PATH="$CURDIR/debian/tmp/usr/lib/$DEB_HOST_MULTIARCH"
     exec "$BUILT_FILE" \
         -m "$CURDIR/debian/tmp/usr/share/file/magic.mgc" \