Revert "mesa: Require mipmap completeness for glCopyImageSubData(), sometimes."

Revert "mesa: Require mipmap completeness for glCopyImageSubData(), sometimes."

This reverts commit c5bf7cb52942cb7df9f5d73746ffbf3c102d12cc.

This broke rendering in "Total War: WARHAMMER", which uses a single
level RGBA_UINT32 texture and the default filter modes of GL_LINEAR
and GL_NEAREST_MIPMAP_LINEAR.  However, the texture max level is 0,
so it is actually mipmap complete - it's the integer + linear rule
that causes the error.

I'm working with Khronos to find a real solution.  However it turns
out, this patch is not correct and breaks real programs, so let's
revert it for now.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100690
Bugzilla: https://cvs.khronos.org/bugzilla/show_bug.cgi?id=16224
Cc: "17.1" <mesa-stable@lists.freedesktop.org>