TravisCI: Don't run tests with race.

This modifies the goclean.sh script that is executed on Travis to
only run the tests without the race detector.

While it is nice to run the race detector on the tests, unfortunately
there is a limit to the number of goroutines that can be launched while
running it.  Since Travis is now much slower than it once was, this
causes a ton of false positive failures.

goclean.sh

@@ -5,7 +5,6 @@
 # 3. go vet        (http://golang.org/cmd/vet)
 # 4. gosimple      (https://github.com/dominikh/go-simple)
 # 5. unconvert     (https://github.com/mdempsky/unconvert)
-# 6. race detector (http://blog.golang.org/race-detector)
 #
 # gometalinter (github.com/alecthomas/gometalinter) is used to run each static
 # checker.
@@ -36,4 +35,4 @@ test -z "$(gometalinter -j 4 --disable-all \
 --enable=gosimple \
 --enable=unconvert \
 --deadline=10m $linter_targets 2>&1 | grep -v 'ALL_CAPS\|OP_' 2>&1 | tee /dev/stderr)"
-env GORACE="halt_on_error=1" go test -race -tags rpctest $linter_targets
+go test -tags rpctest $linter_targets