Obsolete Solaris 10 support

[Rainer Orth]

As already discussed almost a year ago

	https://sourceware.org/ml/gdb/2018-10/msg00027.html

I'm going to remove Solaris 10 support from GDB for the GDB 9.1.0
release.  While I don't expect any opposition to occur this time, this
is the formal heads-up following our procedure documented at

	https://sourceware.org/gdb/wiki/Internals%20Obsoleting-code

I'm going to post the actual removal patch in a bit, as well as the
proposal to gdb-announce in about a week from now.

	Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University