Windows: don't concatenate to etc/julia/juliarc.jl in make dist

This is already concatenated into as a prerequisite of `make release`,
and copied over by `make install` on line 235. There are 2 copies of
the `let user_data_dir` block in the distribution folder.

Unlike the Mac version which only goes into `make dist`, on Windows this
block goes into juliarc even for the not-yet-installed copy in `usr/etc/julia`.