As far as I know, it is not possible without customizing the sharepoint template (list definition) for the Calendar list.
Can you explain me how to do it in harepoint template (list definition) for the Calendar list.
Please refer to the out of the box list definition feature:
(12\TEMPLATE\FEATURES\EventLists)
Do not modify the files in this directory... if you wish to create your own feature, then simply copy/paste the contents to a new directory in FEATURES (and change the feature GUID), or add the contents to your Visual Studio project (depends on how you want to deploy).
You will need to modify the schema.xml file in the \Events directory. You can refer to this link to help you with that:
for hiding something like that you might want to look at a more lightweight solution like jquery or CSS. unfortunately I can't see the rendered html code at the moment but if ou are familiar jquery or css id imagine it wouldnt be that difficult.