Easy enough. All you need to do is remove the block that is inserted via the paypal.xml You can do this via your custom theme local.xml file located in your layout folder.
Thus if you look at /app/design/frontend/base/default/layout/paypal.xml
you will find the directive that places that link in this block:
<default>
<reference name="topCart.extra_actions">
<block type="paypal/express_shortcut" name="paypal.partner.top_cart.shortcut" template="paypal/express/shortcut.phtml"/>
</reference>
<reference name="cart_sidebar.extra_actions">
<block type="paypal/express_shortcut" name="paypal.partner.cart_sidebar.shortcut" template="paypal/express/shortcut.phtml"/>
</reference>
</default>
Thus to remove, in your local.xml theme file you can place:
<default>
<!-- remove from top cart -->
<reference name="topCart.extra_actions">
<remove name="paypal.partner.top_cart.shortcut"/>
</reference>
<!-- remove from sidebar -->
<reference name="cart_sidebar.extra_actions">
<remove name="paypal.partner.cart_sidebar.shortcut"/>
</reference>
</default>