[turbofan] Remove dead {is_liveness_analysis_enabled}.

src/compiler/bytecode-graph-builder.cc

Index: src/compiler/bytecode-graph-builder.cc
diff --git a/src/compiler/bytecode-graph-builder.cc b/src/compiler/bytecode-graph-builder.cc
index 5a596e2f45c612a47bc3b14b367a2dad94f6968c..385efaa9de20ba51ab86130b1dd03872240d1bb8 100644
--- a/src/compiler/bytecode-graph-builder.cc
+++ b/src/compiler/bytecode-graph-builder.cc
@@ -470,7 +470,6 @@ BytecodeGraphBuilder::BytecodeGraphBuilder(
       input_buffer_size_(0),
       input_buffer_(nullptr),
       exit_controls_(local_zone),
-      is_liveness_analysis_enabled_(FLAG_analyze_environment_liveness),
       state_values_cache_(jsgraph),
       source_positions_(source_positions),
       start_position_(shared_info->start_position(), inlining_id) {}