Move subreason_strs and subtype_strs to subscriberfuncs.c.

Move subreason_strs and subtype_strs to subscriberfuncs.c.
They are needed by multiple executables, so can't go in a file with main(). It
is important to remember to link in subscriberfuncs.c whenever these variables
are used. Maybe write wrapper functions in future to enforce this as errors can
be hard to track down when this goes wrong.