opkg: backport upstream fixes, code cleanups

Update to latest Git in order to import the following fixes:

1d0263b check_data_file_clashes_change: remove duplicated offline root in paths
a00a6a9 buildReplaces: do not add duplicated replacees
9fbedd8 opkg: compare-versions doesn't need any state
45b54f6 opkg_cmd: fix segmentation fault in opkg_compare_versions_cmd()
93de62b opkg_cmd: fix return of opkg compare-versions
51275a8 pkg_src_list_push: remove unused function
947d3d4 pkg_src_list_pop: remove unused function
980cfb2 str_list_push: remove unused function
52c31c1 str_list_prev: remove unused function
7d24212 str_list_last: remove unused function
48142a3 conffile_list_pop: remove unused function
46c5de5 pkg_dest_list_push: remove unused functions
368bb62 nv_pair_list_prev: remove unused function
2985c00 nv_pair_list_last: remove unused function
f5082ac conffile_list_pop: remove unused function
89bf8b9 conffile_list_push: remove unused function
23d31fb active_list_sort: remove unused function
7fe45f2 active_list_add_depend: remove unused function
86b584d pkg_dependence_satisfied: remove unused function
816d330 Fix typo in pkg_hash_fetch_best_installation_candidate.
07f3b02 set_flags_from_control: remove function

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

package/system/opkg/Makefile

@@ -16,9 +16,9 @@ PKG_FLAGS:=essential
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL:=https://git.lede-project.org/project/opkg-lede.git
-PKG_SOURCE_DATE:=2017-03-15
-PKG_SOURCE_VERSION:=cfe46c7d5787df0bd643d44e8f985107b562300e
-PKG_MIRROR_HASH:=abc0c125c856318a457add3d2c5ec668464ed962ccfc688ea1cbd5047b435f23
+PKG_SOURCE_DATE:=2017-03-23
+PKG_SOURCE_VERSION:=1d0263bb40e3c099501fc1f2431907636230e7f2
+PKG_MIRROR_HASH:=1f527179e60b9404affa5f3c9c506d4249e085bf521f770819b8648273a1010c
 
 PKG_LICENSE:=GPL-2.0
 PKG_LICENSE_FILES:=COPYING