Remove default clause in minor switch statements

Bending to clang warnings...
https://bugs.chromium.org/p/chromium/issues/detail?id=593057

src/hb-ot-shape-complex-indic.cc

diff --git a/src/hb-ot-shape-complex-indic.cc b/src/hb-ot-shape-complex-indic.cc
index c8fc2b5..1e151a7 100644
--- a/src/hb-ot-shape-complex-indic.cc
+++ b/src/hb-ot-shape-complex-indic.cc
@@ -742,10 +742,6 @@
 
     switch (indic_plan->config->base_pos)
     {
-      default:
-        assert (false);
-	HB_FALLTHROUGH;
-
       case BASE_POS_LAST:
       {
 	/* -> starting from the end of the syllable, move backwards */

src/hb-ot-shape-complex-thai.cc

diff --git a/src/hb-ot-shape-complex-thai.cc b/src/hb-ot-shape-complex-thai.cc
index 58392b6..4322b0d 100644
--- a/src/hb-ot-shape-complex-thai.cc
+++ b/src/hb-ot-shape-complex-thai.cc
@@ -139,7 +139,6 @@
   };
 
   switch (action) {
-    default: assert (false); HB_FALLTHROUGH;
     case NOP: return u;
     case SD:  pua_mappings = SD_mappings; break;
     case SDL: pua_mappings = SDL_mappings; break;