[indic] Do NOT allow matra after Halant,ZWJ

Fixes https://github.com/harfbuzz/harfbuzz/issues/556

Devanagari regresses 12 tests, and Gujarati 2.  See:

  https://github.com/harfbuzz/harfbuzz/issues/556#issuecomment-419957472

New numbers:

BENGALI: 353725 out of 354188 tests passed. 463 failed (0.130722%)
DEVANAGARI: 707299 out of 707394 tests passed. 95 failed (0.0134296%)
GUJARATI: 366353 out of 366457 tests passed. 104 failed (0.0283799%)
GURMUKHI: 60729 out of 60747 tests passed. 18 failed (0.0296311%)
KANNADA: 951300 out of 951913 tests passed. 613 failed (0.0643966%)
MALAYALAM: 1048136 out of 1048334 tests passed. 198 failed (0.0188871%)
ORIYA: 42327 out of 42329 tests passed. 2 failed (0.00472489%)
SINHALA: 271596 out of 271847 tests passed. 251 failed (0.0923313%)
TAMIL: 1091754 out of 1091754 tests passed. 0 failed (0%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)

src/hb-ot-shape-complex-indic-machine.rl

@@ -69,7 +69,7 @@ syllable_tail = (z?.SM.SM?.ZWNJ?)? A{0,3}?;
 halant_group = (z?.H.(ZWJ.N?)?);
 final_halant_group = halant_group | H.ZWNJ;
 medial_group = CM?;
-halant_or_matra_group = (final_halant_group | (H.ZWJ)? matra_group{0,4});
+halant_or_matra_group = (final_halant_group | matra_group{0,4});
 
 
 consonant_syllable =	(Repha|CS)? (cn.halant_group){0,4} cn medial_group halant_or_matra_group syllable_tail;