Remove some unused and unneeded flags.

src/flag-definitions.h

Index: src/flag-definitions.h
===================================================================
--- src/flag-definitions.h	(revision 9575)
+++ src/flag-definitions.h	(working copy)
@@ -300,9 +300,6 @@
 DEFINE_bool(canonicalize_object_literal_maps, true,
             "Canonicalize maps for object literals.")
 
-DEFINE_bool(use_big_map_space, true,
-            "Use big map space, but don't compact if it grew too big.")
-
 DEFINE_int(max_map_space_pages, MapSpace::kMaxMapPageIndex - 1,
            "Maximum number of pages in map space which still allows to encode "
            "forwarding pointers.  That's actually a constant, but it's useful "
@@ -338,7 +335,6 @@
 
 // Regexp
 DEFINE_bool(regexp_optimization, true, "generate optimized regexp code")
-DEFINE_bool(regexp_entry_native, true, "use native code to enter regexp")
 
 // Testing flags test/cctest/test-{flags,api,serialization}.cc
 DEFINE_bool(testing_bool_flag, true, "testing_bool_flag")
@@ -465,9 +461,6 @@
 
 DEFINE_bool(trace_isolates, false, "trace isolate state changes")
 
-DEFINE_bool(trace_live_byte_count, false,
-            "trace updates to page live byte count")
-
 // VM state
 DEFINE_bool(log_state_changes, false, "Log state changes.")