Revise NEWS description of changes to gettimeofday etc.

Mostly English grammar and style improvements.  The bullet list is
reorganized a little for clarity.  The details of exactly which
Linux-based ports still report system-wide time zone information
from gettimeofday has been removed, as this is not intended to be
something people should rely on.

Also clarify the deprecation of older SPARC ISAs, based on the fact
that “SPARC version 7” is actually the very first version of the SPARC
ISA (Sun Microsystems was very fond of letting the marketing
department pick version numbers).

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>