deps: V8: remove references to non-existent flags

nodejs#49703 cherry-picked a commit from
upstream V8 which references some maglev-related flags that are not
present in the version of V8 in Node.js 20.

Author: richardlau

common.gypi

@@ -36,7 +36,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.19',
+    'v8_embedder_string': '-node.20',
 
     ##### V8 defaults for Node.js #####
 

deps/v8/src/flags/flags.cc

@@ -586,10 +586,6 @@ uint32_t ComputeFlagListHash() {
     // The following flags are implied by --predictable (some negated).
     if (flag.PointsTo(&v8_flags.concurrent_sparkplug) ||
         flag.PointsTo(&v8_flags.concurrent_recompilation) ||
-#ifdef V8_ENABLE_MAGLEV
-        flag.PointsTo(&v8_flags.maglev_deopt_data_on_background) ||
-        flag.PointsTo(&v8_flags.maglev_build_code_on_background) ||
-#endif
         flag.PointsTo(&v8_flags.parallel_scavenge) ||
         flag.PointsTo(&v8_flags.concurrent_marking) ||
         flag.PointsTo(&v8_flags.concurrent_array_buffer_sweeping) ||