unpack: don't wipe build stamps

That's the job of the clean script, don't force a rebuild after
build & autoremove & unpack

scripts/unpack

@@ -206,8 +206,6 @@ if [ "${PKG_SECTION}" != "virtual" ]; then
   mkdir -p "${PKG_BUILD}"
   echo "INFO_PKG_NAME=\"${PKG_NAME}\"" > "${PKG_BUILD}/.libreelec-package"
 
-  rm -f ${STAMPS}/${PKG_NAME}/build_*
-
   PKG_DEEPHASH=$(calculate_stamp)
   for i in PKG_NAME PKG_DEEPHASH; do
     echo "STAMP_${i}=\"${!i}\"" >> ${STAMP}