firmware: delete pointlessly cached (large) file after use

the archive content file downloaded to obtain a list of firmware packages
is always deleted and downloaded afresh currently. it may not be ideal that
we do not make use of the cache here, however while that remains
unaddressed, we might as well delete the file after we've used it in order
to not pointlessly waste disk space.

note that this file is ~613 MB for sid-amd64 currently.

Gbp-Dch: Short
Closes: #952907

scripts/build/chroot_firmware

@@ -107,6 +107,8 @@ then
 	FIRMWARE_PACKAGES="${FIRMWARE_PACKAGES} $(awk '/^lib\/firmware/ { print $2 }' "${CONTENTS_FILE}" | sort -u)"
 fi
 
+rm -f "${CONTENTS_FILE}"
+
 # Drop section and keep package names only
 for _PACKAGE in ${FIRMWARE_PACKAGES}
 do

scripts/build/installer_debian-installer

@@ -395,6 +395,8 @@ then
 			FIRMWARE_PACKAGES="${FIRMWARE_PACKAGES} $(awk '/^lib\/firmware/ { print $2 }' "${CONTENTS_FILE}" | sort -u)"
 		fi
 
+		rm -f "${CONTENTS_FILE}"
+
 		# Drop section and keep package names only
 		for _PACKAGE in ${FIRMWARE_PACKAGES}
 		do