The gimp_procedure_run() already existed, though it was with an ordered
GimpValueArray array of arguments. Its usage feels redundant to the series of
gimp_pdb_run_procedure*() functions (which is confusing), but
gimp_procedure_run() was actually a bit more generic, because it does not
necessarily calls GimpProcedure-s through the PDB! For instance, it can runs a
local GimpProcedure, such as the case of one procedure which would want to call
another procedure in the same plug-in, but without having to go through PDB. Of
course, for local code, you may as well run relevant functions directly, yet it
makes sense that if one of the redundant-looking function is removed, it should
be the more specific one. Also gimp_procedure_run() feels a lot simpler and
logical, API wise.

A main difference in usage is that now, plug-in developers have to first
explicitly look up the GimpPdbProcedure with gimp_pdb_lookup_procedure() when
they wish to call PDB procedures on the wire. This was done anyway in the
gimp_pdb_run_procedure*() code, now it's explicit (rather than calling by name
directly).

Concretely:

* gimp_pdb_run_procedure(), gimp_pdb_run_procedure_config() and
  gimp_pdb_run_procedure_valist() are removed.
* gimp_procedure_run() API is modified to use a variable args list instead of a
  GimpValueArray.
* gimp_procedure_run_config() and gimp_procedure_run_valist() are added.
* gimp_procedure_run_config() in particular will be the one used in bindings
  which don't have variable args support through a (rename-to
  gimp_procedure_run) annotation.