sstate.bbclass: drop obsolete codes

The SSTATECLEANFUNCS mechanism was introduced to solve user/group
deletion problem. After RSS mechanism was introduced, there's no
need to do so.

There was a patch to remove these obsolete codes for useradd.bbclass,
but the codes in sstate.bbclass were not removed. So clean it up.

(From OE-Core rev: 215b83ce892a7002ed0b1bd7b82a08e67ae15121)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/sstate.bbclass

@@ -59,7 +59,6 @@ SSTATEPREINSTFUNCS = ""
 SSTATEPOSTUNPACKFUNCS = "sstate_hardcode_path_unpack"
 SSTATEPOSTINSTFUNCS = ""
 EXTRA_STAGING_FIXMES ?= "HOSTTOOLS_DIR"
-SSTATECLEANFUNCS = ""
 
 # Check whether sstate exists for tasks that support sstate and are in the
 # locked signatures file.
@@ -507,10 +506,6 @@ def sstate_clean(ss, d):
                 stfile.endswith(rm_nohash):
             oe.path.remove(stfile)
 
-    # Removes the users/groups created by the package
-    for cleanfunc in (d.getVar('SSTATECLEANFUNCS') or '').split():
-        bb.build.exec_func(cleanfunc, d)
-
 sstate_clean[vardepsexclude] = "SSTATE_MANFILEPREFIX"
 
 CLEANFUNCS += "sstate_cleanall"