Revert "Added CustomNode icon in startPage"

Reverts DynamoDS/Dynamo#2632 

1) Test Failure : Dynamo.Tests.DynamoSamples.Core_Strings
     Expected: 37
  But was:  31

at Dynamo.Tests.DynamoSamples.Core_Strings() in c:\EC\Dynamo\master\test\Libraries\WorlflowTests\DynamoSamples.cs:line 486

2) Test Failure : Dynamo.Tests.DynamoSamples.ImportExport_CSV_to_Stuff
     Expected: 16
  But was:  14

at Dynamo.Tests.DynamoSamples.ImportExport_CSV_to_Stuff() in c:\EC\Dynamo\master\test\Libraries\WorlflowTests\DynamoSamples.cs:line 518