Remove error when calling glGenQueries/glDeleteQueries while a query is active

Remove error when calling glGenQueries/glDeleteQueries while a query is active

There is nothing in the OpenGL specification which prevents the user from
calling glGenQueries to generate a new query object while another object is
active. Neither is there anything in the Mesa implementation which prevents
this. So remove the INVALID_OPERATION errors in this case.

Similarly, it is explicitly allowed by the OpenGL specification to delete an
active query, so remove the assertion for that case, replacing it with the
necesssary state updates to end the query, (clear the bindpt pointer and call
into the driver's EndQuery hook).

CC: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Brian Paul <brianp@vmware.com>
Tested-by: Brian Paul <brianp@vmware.com>