[snapshot] Do not verify the checksum

As we don't need it, and the added overhead becomes significant on large
snapshots.

src/snapshot/mksnapshot.cc

@@ -87,7 +87,7 @@ class SnapshotFileWriter {
     fprintf(
         fp,
         "bool Snapshot::ShouldVerifyChecksum(const v8::StartupData* data) {\n");
-    fprintf(fp, "  return true;\n");
+    fprintf(fp, "  return false;\n");
     fprintf(fp, "}\n");
     fprintf(fp, "}  // namespace internal\n");
     fprintf(fp, "}  // namespace v8\n");