Fix two tests that could fail when run early in the test run due to side effects.

Author: rstam

tests/MongoDB.Bson.Tests/ObjectModel/LazyBsonArrayTests.cs

@@ -628,7 +628,6 @@ public void TestLargeArrayDeserialization()
  }
  bsonDocument.Add("arrayfield", bsonArray);
  var bson = bsonDocument.ToBson();
- BsonDefaults.MaxDocumentSize = 4 * 1024 * 1024;
  using (var lazyBsonDocument = BsonSerializer.Deserialize<LazyBsonDocument>(bson))
  {
  Assert.Equal(2, lazyBsonDocument.ElementCount);

tests/MongoDB.Bson.Tests/ObjectModel/LazyBsonDocumentTests.cs

@@ -865,7 +865,6 @@ public void TestLargeDocumentDeserialization()
  bsonDocument.Add("doublefield_"+i, i*1.0);
  }
  var bson = bsonDocument.ToBson();
- BsonDefaults.MaxDocumentSize = 4 * 1024 * 1024;
  using (var lazyBsonDocument = BsonSerializer.Deserialize<LazyBsonDocument>(bson))
  {
  Assert.Equal(noOfDoubleFields + 1, lazyBsonDocument.ElementCount);