cleanup: remove unused certora config

We're using scripts in `certora/scripts`, so I'm removing the config
file from here as we otherwise run into inconsistencies.

certora/certora.conf

@@ -1,15 +0,0 @@
-{
-  "files": [
-    "contracts/tokens/CollectibleV1.sol",
-    "certora/harness/CollectibleV1Harness.sol",
-    "contracts/tokens/OwnerToken.sol",
-    "contracts/tokens/MasterToken.sol"
-  ],
-  "msg": "Verifying CollectibleV1.sol",
-  "rule_sanity": "basic",
-  "verify": "CollectibleV1Harness:certora/specs/CollectibleV1.spec",
-  "link": ["CollectibleV1Harness:ownerToken=OwnerToken", "CollectibleV1Harness:masterToken=MasterToken"],
-  "packages": ["@openzeppelin=lib/openzeppelin-contracts"],
-  "optimistic_loop": true,
-  "loop_iter": "3"
-}