Cleanup swift.bzl.
Cleanup swift.bzl.

Removes an old code path that is not relevant anymore.

RELNOTES:

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MOS_MIGRATED_REVID=122534499

mikelalcon/bazel,cushon/bazel,mikelalcon/bazel,kchodorow/bazel-1,Asana/bazel,Asana/bazel,iamthearm/bazel,kchodorow/bazel,ulfjack/bazel,perezd/bazel,juhalindfors/bazel-patches,mikelalcon/bazel,dropbox/bazel,aehlig/bazel,kchodorow/bazel-1,ulfjack/bazel,meteorcloudy/bazel,katre/bazel,zhexuany/bazel,dslomov/bazel,cushon/bazel,mrdomino/bazel,ulfjack/bazel,werkt/bazel,damienmg/bazel,ButterflyNetwork/bazel,dslomov/bazel,damienmg/bazel,variac/bazel,katre/bazel,dslomov/bazel-windows,zhexuany/bazel,iamthearm/bazel,bazelbuild/bazel,snnn/bazel,Asana/bazel,hermione521/bazel,meteorcloudy/bazel,LuminateWireless/bazel,spxtr/bazel,dslomov/bazel-windows,variac/bazel,katre/bazel,kchodorow/bazel-1,perezd/bazel,akira-baruah/bazel,kchodorow/bazel,akira-baruah/bazel,aehlig/bazel,dropbox/bazel,juhalindfors/bazel-patches,LuminateWireless/bazel,aehlig/bazel,davidzchen/bazel,mbrukman/bazel,Asana/bazel,dslomov/bazel,mbrukman/bazel,abergmeier-dsfishlabs/bazel,Asana/bazel,UrbanCompass/bazel,mrdomino/bazel,safarmer/bazel,UrbanCompass/bazel,mrdomino/bazel,zhexuany/bazel,kchodorow/bazel-1,meteorcloudy/bazel,dslomov/bazel,davidzchen/bazel,LuminateWireless/bazel,mikelikespie/bazel,iamthearm/bazel,mikelalcon/bazel,dslomov/bazel-windows,ButterflyNetwork/bazel,LuminateWireless/bazel,abergmeier-dsfishlabs/bazel,akira-baruah/bazel,snnn/bazel,werkt/bazel,kchodorow/bazel,spxtr/bazel,juhalindfors/bazel-patches,mrdomino/bazel,abergmeier-dsfishlabs/bazel,zhexuany/bazel,abergmeier-dsfishlabs/bazel,UrbanCompass/bazel,aehlig/bazel,LuminateWireless/bazel,snnn/bazel,dslomov/bazel,cushon/bazel,kchodorow/bazel,mbrukman/bazel,akira-baruah/bazel,aehlig/bazel,iamthearm/bazel,twitter-forks/bazel,juhalindfors/bazel-patches,snnn/bazel,dslomov/bazel,damienmg/bazel,hermione521/bazel,dropbox/bazel,hermione521/bazel,iamthearm/bazel,mrdomino/bazel,twitter-forks/bazel,bazelbuild/bazel,hermione521/bazel,safarmer/bazel,dropbox/bazel,snnn/bazel,bazelbuild/bazel,werkt/bazel,ButterflyNetwork/bazel,zhexuany/bazel,akira-baruah/bazel,bazelbuild/bazel,hermione521/bazel,dslomov/bazel-windows,twitter-forks/bazel,perezd/bazel,damienmg/bazel,mikelalcon/bazel,katre/bazel,meteorcloudy/bazel,mikelikespie/bazel,akira-baruah/bazel,Asana/bazel,ulfjack/bazel,juhalindfors/bazel-patches,aehlig/bazel,mikelalcon/bazel,perezd/bazel,mbrukman/bazel,UrbanCompass/bazel,mikelikespie/bazel,snnn/bazel,UrbanCompass/bazel,UrbanCompass/bazel,safarmer/bazel,katre/bazel,mbrukman/bazel,davidzchen/bazel,ButterflyNetwork/bazel,Asana/bazel,katre/bazel,spxtr/bazel,kchodorow/bazel-1,abergmeier-dsfishlabs/bazel,dslomov/bazel,perezd/bazel,dropbox/bazel,hermione521/bazel,dropbox/bazel,zhexuany/bazel,dslomov/bazel-windows,ulfjack/bazel,meteorcloudy/bazel,safarmer/bazel,mrdomino/bazel,kchodorow/bazel,ButterflyNetwork/bazel,variac/bazel,mikelikespie/bazel,damienmg/bazel,werkt/bazel,twitter-forks/bazel,bazelbuild/bazel,perezd/bazel,mikelikespie/bazel,spxtr/bazel,damienmg/bazel,cushon/bazel,juhalindfors/bazel-patches,spxtr/bazel,iamthearm/bazel,variac/bazel,kchodorow/bazel,variac/bazel,ButterflyNetwork/bazel,spxtr/bazel,snnn/bazel,kchodorow/bazel-1,safarmer/bazel,davidzchen/bazel,mbrukman/bazel,variac/bazel,abergmeier-dsfishlabs/bazel,safarmer/bazel,ulfjack/bazel,twitter-forks/bazel,mikelikespie/bazel,werkt/bazel,davidzchen/bazel,perezd/bazel,davidzchen/bazel,damienmg/bazel,spxtr/bazel,werkt/bazel,dslomov/bazel-windows,juhalindfors/bazel-patches,variac/bazel,cushon/bazel,LuminateWireless/bazel,aehlig/bazel,bazelbuild/bazel,davidzchen/bazel,twitter-forks/bazel,meteorcloudy/bazel,cushon/bazel,twitter-forks/bazel,ulfjack/bazel,kchodorow/bazel,meteorcloudy/bazel