[test] We don’t care about glyph positions here

Freetype and OT font functions give different positions for some glyphs
in this font (OT seems to be correct), but that is not what we are
interested in in this test.

See https://github.com/behdad/harfbuzz/pull/590#issuecomment-341045223.

test/shaping/tests/cluster.tests

-fonts/sha1sum/6466d38c62e73a39202435a4f73bf5d6acbb73c0.ttf:--cluster-level=2:U+0078,U+030A,U+0058,U+030A:[gid2=0+1083|gid4=1@-555,-8+0|gid1=2+1200|gid4=3@-614,349+0]
-fonts/sha1sum/43ef465752be9af900745f72fe29cb853a1401a5.ttf:--cluster-level=1:U+05D4,U+05B7,U+05E9,U+05BC,U+05C1,U+05B8,U+05DE,U+05B4,U+05DD:[uni05DD=8+1359|uni05B4=7@111,0+0|uni05DE=6+1391|uni05B8=5+0|uni05BC=3+0|uni05C1=3+0|uni05E9=2+1451|uni05B7=1@28,0+0|uni05D4=0+1338]
+fonts/sha1sum/6466d38c62e73a39202435a4f73bf5d6acbb73c0.ttf:--cluster-level=2 --no-positions:U+0078,U+030A,U+0058,U+030A:[gid2=0|gid4=1|gid1=2|gid4=3]
+fonts/sha1sum/43ef465752be9af900745f72fe29cb853a1401a5.ttf:--cluster-level=1 --no-positions:U+05D4,U+05B7,U+05E9,U+05BC,U+05C1,U+05B8,U+05DE,U+05B4,U+05DD:[uni05DD=8|uni05B4=7|uni05DE=6|uni05B8=5|uni05BC=3|uni05C1=3|uni05E9=2|uni05B7=1|uni05D4=0]