contracts-bedrock: delete dead SystemConfig code

The old constant for the min gas limit was left behind
in the PR that made the min gas limit calculation safe.
This commit deletes the constant and updates the tests
to use the new method.

packages/contracts-bedrock/.gas-snapshot

@@ -418,7 +418,7 @@ SequencerFeeVault_Test:test_withdraw_succeeds() (gas: 163228)
 SetPrevBaseFee_Test:test_setPrevBaseFee_succeeds() (gas: 11515)
 StandardBridge_Stateless_Test:test_isCorrectTokenPair_succeeds() (gas: 49936)
 StandardBridge_Stateless_Test:test_isOptimismMintableERC20_succeeds() (gas: 33072)
-SystemConfig_Initialize_TestFail:test_initialize_lowGasLimit_reverts() (gas: 148858)
+SystemConfig_Initialize_TestFail:test_initialize_lowGasLimit_reverts() (gas: 148848)
 SystemConfig_Setters_TestFail:test_setBatcherHash_notOwner_reverts() (gas: 10546)
 SystemConfig_Setters_TestFail:test_setGasConfig_notOwner_reverts() (gas: 10622)
 SystemConfig_Setters_TestFail:test_setGasLimit_notOwner_reverts() (gas: 10615)
@@ -427,6 +427,6 @@ SystemConfig_Setters_TestFail:test_setResourceConfig_badPrecision_reverts() (gas
 SystemConfig_Setters_TestFail:test_setResourceConfig_lowGasLimit_reverts() (gas: 16082)
 SystemConfig_Setters_TestFail:test_setResourceConfig_notOwner_reverts() (gas: 11790)
 SystemConfig_Setters_TestFail:test_setResourceConfig_zeroDenominator_reverts() (gas: 13039)
-SystemConfig_Setters_TestFail:test_setUnsafeBlockSigner_notOwner_reverts() (gas: 10639)
+SystemConfig_Setters_TestFail:test_setUnsafeBlockSigner_notOwner_reverts() (gas: 10616)
 TransferOnionTest:test_constructor_succeeds() (gas: 564855)
 TransferOnionTest:test_unwrap_succeeds() (gas: 724958)
\ No newline at end of file

packages/contracts-bedrock/contracts/L1/SystemConfig.sol

@@ -42,13 +42,6 @@ contract SystemConfig is OwnableUpgradeable, Semver {
      */
     bytes32 public constant UNSAFE_BLOCK_SIGNER_SLOT = keccak256("systemconfig.unsafeblocksigner");
 
-    /**
-     * @notice Minimum gas limit. This should not be lower than the maximum deposit gas resource
-     *         limit in the ResourceMetering contract used by OptimismPortal, to ensure the L2
-     *         block always has sufficient gas to process deposits.
-     */
-    uint64 public constant MINIMUM_GAS_LIMIT = 8_000_000;
-
     /**
      * @notice Fixed L2 gas overhead. Used as part of the L2 fee calculation.
      */
@@ -87,7 +80,7 @@ contract SystemConfig is OwnableUpgradeable, Semver {
     event ConfigUpdate(uint256 indexed version, UpdateType indexed updateType, bytes data);
 
     /**
-     * @custom:semver 1.1.0
+     * @custom:semver 1.2.0
      *
      * @param _owner             Initial owner of the contract.
      * @param _overhead          Initial overhead value.
@@ -105,7 +98,7 @@ contract SystemConfig is OwnableUpgradeable, Semver {
         uint64 _gasLimit,
         address _unsafeBlockSigner,
         ResourceMetering.ResourceConfig memory _config
-    ) Semver(1, 1, 0) {
+    ) Semver(1, 2, 0) {
         initialize({
             _owner: _owner,
             _overhead: _overhead,

packages/contracts-bedrock/contracts/test/SystemConfig.t.sol

@@ -176,7 +176,7 @@ contract SystemConfig_Setters_Test is SystemConfig_Init {
     }
 
     function testFuzz_setGasLimit_succeeds(uint64 newGasLimit) external {
-        uint64 minimumGasLimit = sysConf.MINIMUM_GAS_LIMIT();
+        uint64 minimumGasLimit = sysConf.minimumGasLimit();
         newGasLimit = uint64(
             bound(uint256(newGasLimit), uint256(minimumGasLimit), uint256(type(uint64).max))
         );

packages/contracts-bedrock/contracts/test/invariants/SystemConfig.t.sol

@@ -42,6 +42,6 @@ contract SystemConfig_GasLimitLowerBound_Invariant is Test {
      * than the hard-coded lower bound.
      */
     function invariant_gasLimitLowerBound() external {
-        assertTrue(config.gasLimit() >= config.MINIMUM_GAS_LIMIT());
+        assertTrue(config.gasLimit() >= config.minimumGasLimit());
     }
 }