Switch to our hermetic bc.

Test: treehugger
Change-Id: I12142a7f54190edd21e719bbd8f5df831ada6161
diff --git a/ui/build/paths/config.go b/ui/build/paths/config.go
index 909d93c..f347a11 100644
--- a/ui/build/paths/config.go
+++ b/ui/build/paths/config.go
@@ -75,7 +75,6 @@
 
 var Configuration = map[string]PathConfig{
 	"bash":     Allowed,
-	"bc":       Allowed,
 	"dd":       Allowed,
 	"diff":     Allowed,
 	"dlv":      Allowed,