Remove const from many struct objfile *

Remove const from many struct objfile *

I am just not sure if we should go the route of
        struct objfile * -> const struct objfile *
or the other way of:
        const struct objfile * -> struct objfile *

Normally const adding is better but here I do not see much useful to have any
struct objfile * const and then it just causes pointer compatibility problems.

On Wed, 03 Dec 2014 18:18:44 +0100, Doug Evans wrote:
struct objfile is one case where I've decided to just leave the const
out and not worry about it.

gdb/ChangeLog
2014-12-05  Jan Kratochvil  <jan.kratochvil@redhat.com>

	Remove const from struct objfile *.
	* solib-darwin.c, solib-spu.c, solib-svr4.c, solib.c, solist.h,
	symtab.c, symtab.h: In these files.