Bug 1455143 - Don't remove common test archive; r=ted

This target is a prereq for all test archives. Why we only remove a
single test archive, I don't know. We always build this test archive.
So it should always get overwritten and we don't need to remove an
existing file.

MozReview-Commit-ID: 1qd1T3w6kVT

--HG--
extra : rebase_source : ab27910a45961da636a4077952a2d67819ad701b

testing/testsuite-targets.mk

@@ -144,7 +144,6 @@ test-packages-manifest:
       $(foreach pkg,$(TEST_PKGS_TARGZ),$(call PKG_ARG,$(pkg),tar.gz))
 
 package-tests-prepare-dest:
-	@rm -f '$(DIST)/$(PKG_PATH)$(TEST_PACKAGE)'
 	$(NSINSTALL) -D $(DIST)/$(PKG_PATH)
 
 define package_archive