L2: prevent unnecesary storage modifications during contract updates

[avilagaston9]

Currently, our system contracts updater constantly modifies fixtures/genesis/l2.json due to changes in the order of the storage keys:

-        "0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103": "0xf000",
-        "0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc": "0xeffe"
+        "0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc": "0xeffe",
+        "0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103": "0xf000"

We should prevent this from happening, as we are committing this file in all PRs.