Remove sum(1) from the list of approved binaries.

No-one should be using BSD sum in 2018.

Bug: N/A
Test: treehugger
Change-Id: I9aa313e111217a2d73ba41eaf49035d8293b5785
diff --git a/ui/build/paths/config.go b/ui/build/paths/config.go
index ef6fd5f..8c51641 100644
--- a/ui/build/paths/config.go
+++ b/ui/build/paths/config.go
@@ -134,7 +134,6 @@
 	"sleep":     Allowed,
 	"sort":      Allowed,
 	"stat":      Allowed,
-	"sum":       Allowed,
 	"tar":       Allowed,
 	"tail":      Allowed,
 	"tee":       Allowed,