Makefile `r_build` target is sometimes used inappropriately

[nmdefries]

In the Makefile, the r_build target is listed as a dependency of the score_forecast target and the contained docker run call does use the forecast-eval-build image created in r_build -- great. The start_dev target, on the other hand, has r_build as a dependency but uses an entirely different image. It looks like the r_build dependency is completely extraneous.