runtime: delete export_arm_test.go

The only thing export_arm_test.go does is to export usplit,
which does not exist in gccgo.

Change-Id: If459299d8b4402ca28bb0e1934f56ffe6723e0bd
Reviewed-on: https://go-review.googlesource.com/c/155760
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed