convert some gvprintf calls with no format codes to gvputs

convert some gvprintf calls with no format codes to gvputs

This is equivalent, but gvputs is less expensive to call than gvprintf.
Surprisingly,¹ with link-time optimization a compiler is able to see this
optimization for itself, so this makes no difference to performance in an LTO
build. However, this should be a slight optimization in non-LTO builds.

¹ I say surprisingly because compilers generally do not attempt inter-procedural
  optimization across varargs calls. The calling convention and interpretation
  of arguments is complex enough that they generally conservatively leave such
  calls alone.