Fix NEWS formatting in GDB 8.0 section

Fix NEWS formatting in GDB 8.0 section

Change the GDB 8.0 section of the NEWS file to try to follow this order:

  * Functional changes
  * Added and removed configurations and targets
  * New commands
  * New options
  * MI changes

In particular, there were two "New commands" sections.

gdb/ChangeLog:

	* NEWS (Changes in GDB 8.0): Remove extra empty line.  Move
	"Removed targets and native configurations" up.  Merge duplicate
	"New commands" sub-sections.  Add "New options" sub-sections.