Removed child-drawer checks

[valerybugakov]

Hey, I was trying to use two nested drawers like this:

<Drawer 
  content={
    <Drawer content={channels}>{menu}</Drawer>
  }
>
  {children}
</Drawer>

When user tries to close nested drawer, when the parent drawer is opened, removed checks prevented him from doing that. I dug into commits and issues related to this topic and it seems that those checks are optimized for nesting via children (not content prop):

<Drawer content={menu}>
  <Drawer content={channels}>{children}</Drawer>
</Drawer>

Actually it's possible to implement required behavior using conditional values in panCloseMask and panOpenMask depending on open state of drawers, so those checks are not necessary. Please let me know if I missed anything here.