[packages] git: get rid of XDL_FAST_HASH, it does NOT work on big-endian systems,
and uname is no reliable way to determine which arch will run git 
closes #13611


git-svn-id: svn://svn.openwrt.org/openwrt@37239 3c298f89-4303-0410-b956-a3cf2f4a3e73