Remove broken linter rule.

(cherry picked from commit 3112c1b95e)

.solhint.json

@@ -6,6 +6,7 @@
     "bracket-align": false,
     "compiler-fixed": false,
     "no-simple-event-func-name": false,
+    "separate-by-one-line-in-contract": false,
     "two-lines-top-level-separator": false
   }
 }