fix(run): remove `BAZEL_GEN_DIR` base for `--get`

The ideal was that this would use the generation directory
as the base for the local path to ease
the definition of `--get`.

However, `BAZEL_GEN_DIR` does not exist...and never has.
It was confused with `$(RULEDIR)` which is only a Make
variable and never enters the environment.

Removing as this could lead to Hyrum's law and start
being depended on.