Remove process.emitWarning because it breaks AppVeyor builds

See Level/leveldown#660

test/common.js

@@ -1,9 +1,6 @@
-var warned = false
-
 function testCommon (options) {
   var factory = options.factory
   var test = options.test
-  var clear = !!options.clear
 
   if (typeof factory !== 'function') {
     throw new TypeError('factory must be a function')
@@ -13,15 +10,6 @@ function testCommon (options) {
     throw new TypeError('test must be a function')
   }
 
-  if (!clear && !warned) {
-    warned = true
-    warn(
-      'A next major release of abstract-leveldown will make support of ' +
-      'clear() mandatory. Prepare by enabling the tests and implementing a ' +
-      'custom _clear() if necessary. See the README for details.'
-    )
-  }
-
   return {
     test: test,
     factory: factory,
@@ -32,15 +20,7 @@ function testCommon (options) {
     errorIfExists: options.errorIfExists !== false,
     snapshots: options.snapshots !== false,
     seek: options.seek !== false,
-    clear: clear
-  }
-}
-
-function warn (msg) {
-  if (typeof process !== 'undefined' && process && process.emitWarning) {
-    process.emitWarning(msg)
-  } else if (typeof console !== 'undefined' && console && console.warn) {
-    console.warn('Warning: ' + msg)
+    clear: !!options.clear
   }
 }