cmd/release: don't remove pkg when building race detector
cmd/release: don't remove pkg when building race detector

Fixes golang/go#13664.

Change-Id: I2d4d3ac833f99e052ee35bdc17a061edac085c83
Reviewed-on: https://go-review.googlesource.com/18017
Reviewed-by: Minux Ma <72d850dbd8858b791995463d8539b5a379577f28@golang.org>

proppy/build,golang/build,proppy/build,golang/build,golang/build,proppy/build,golang/build,proppy/build