Makefile: clean up

Makefile: clean up

- Remove unnecessary VCS header detritus

- Indent LIBS assignment to line up with the others

- List source files explicitly

  This prevents the modification of any one file from causing
  make(1) to recompile all modules, and results in a deterministic
  build order.

  The downside is that if a new module is added, the Makefile will
  have to be edited too; but this is no different to the Makefile
  for any other module subdirectory in Atheme proper, and is hardly
  a burden.