[tests/arabic-stch.tests] Don't show flags

We don't need to test the actual flag values.  For unsafe-to-break,
the --verify in run-tests.sh checks what we are interested in.

test/shaping/tests/arabic-stch.tests

-fonts/sha1sum/d9b8bc10985f24796826c29f7ccba3d0ae11ec02.ttf:--no-glyph-names --show-flags:U+0718,U+070F,U+0718,U+0718,U+002E:[1=4+168|3=3+502#1|3=2+502#1|4=1@-1004,0+0#1|5=1@-876,0+0#1|5=1@-799,0+0#1|5=1@-722,0+0#1|5=1@-645,0+0#1|4=1@-566,0+0#1|5=1@-438,0+0#1|5=1@-361,0+0#1|5=1@-284,0+0#1|5=1@-207,0+0#1|4=1@-128,0+0#1|3=0+502]
+fonts/sha1sum/d9b8bc10985f24796826c29f7ccba3d0ae11ec02.ttf:--no-glyph-names:U+0718,U+070F,U+0718,U+0718,U+002E:[1=4+168|3=3+502|3=2+502|4=1@-1004,0+0|5=1@-876,0+0|5=1@-799,0+0|5=1@-722,0+0|5=1@-645,0+0|4=1@-566,0+0|5=1@-438,0+0|5=1@-361,0+0|5=1@-284,0+0|5=1@-207,0+0|4=1@-128,0+0|3=0+502]