[es8] Remove syntactic tail calls support.

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 9d67e627e5e69f151dea840e172d4179dab79cef..62a5f7998ce47d4e6c9a32b6847d6429ae9ace2e 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -2844,7 +2844,6 @@ EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_regexp_lookbehind)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_regexp_named_captures)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_regexp_property)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_function_sent)
-EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_explicit_tailcalls)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_tailcalls)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_restrictive_declarations)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_string_padding)
@@ -3427,7 +3426,6 @@ bool Genesis::InstallNatives(GlobalContextType context_type) {
 
 
 bool Genesis::InstallExperimentalNatives() {
-  static const char* harmony_explicit_tailcalls_natives[] = {nullptr};
   static const char* harmony_tailcalls_natives[] = {nullptr};
   static const char* harmony_sharedarraybuffer_natives[] = {
       "native harmony-atomics.js", NULL};