Remove the --collect-maps flag. Maps should be always collected.

src/flag-definitions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 594 matching lines @@
 DEFINE_BOOL(print_max_heap_committed, false,
             "print statistics of the maximum memory committed for the heap "
             "in name=value format on exit")
 DEFINE_BOOL(trace_gc_verbose, false,
             "print more details following each garbage collection")
 DEFINE_INT(trace_allocation_stack_interval, -1,
            "print stack trace after <n> free-list allocations")
 DEFINE_BOOL(trace_fragmentation, false, "report fragmentation for old space")
 DEFINE_BOOL(trace_fragmentation_verbose, false,
             "report fragmentation for old space (detailed)")
-DEFINE_BOOL(collect_maps, true,
-            "garbage collect maps from which no objects can be reached")
 DEFINE_BOOL(weak_embedded_maps_in_optimized_code, true,
             "make maps embedded in optimized code weak")
 DEFINE_BOOL(weak_embedded_objects_in_optimized_code, true,
             "make objects embedded in optimized code weak")
 DEFINE_BOOL(flush_code, true,
             "flush code that we expect not to use again (during full gc)")
 DEFINE_BOOL(flush_code_incrementally, true,
             "flush code that we expect not to use again (incrementally)")
 DEFINE_BOOL(trace_code_flushing, false, "trace code flushing progress")
 DEFINE_BOOL(age_code, true,
@@ skipping 442 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA