The other option is to use the .webpart file to specify this as the default using the ChromeType property. You can do this in your Visual Studio solution (as below) or you can edit the .webpart file directly in the Web Part Gallery.
As this is a no code approach, it seems a bit simpler than the C# route.
Try this:
<?xml version="1.0" encoding="utf-8"?>
<webParts>
<webPart xmlns="http://schemas.microsoft.com/WebPart/v3">
<metaData>
<type name="<<ClassName>>, $SharePoint.Project.AssemblyFullName$" />
<importErrorMessage>$Resources:core,ImportErrorMessage;</importErrorMessage>
</metaData>
<data>
<properties>
<property name="Title" type="string">Custom List Form</property>
<property name="Description" type="string">Provides A Data Entry Form For a SharePoint List</property>
<!-- SEE CHROME TYPE BELOW -->
<property name="ChromeType" type="chrometype">None</property>
</properties>
</data>
</webPart>
</webParts>