Simplify Solaris port
This should avoid some configuration confusion as exemplified by Jeffrey Walton’s recent bug report (Bug#42675). * configure.ac (opsys): Simplify Solaris configuration by not worrying about Solaris 9 and earlier, as they are no longer supported by the Solaris developers. This should support Walton’s ‘./configure --build=x86_64-sun-solaris’. Instead of bothering with ‘opsys=sol2-6’ and ‘opsys=sol2-10’, just use ‘opsys=solaris’. All uses changed. (emacs_check_sunpro_c): Remove unused var. * doc/misc/tramp.texi (Remote programs): * etc/MACHINES, etc/PROBLEMS: Modernize PATH for Oracle Developer Studio. * etc/PROBLEMS: Move Solaris-related problems to legacy area, except those that are still relevant.