kvdb: exclude anything bbolt related from JS builds

Since bbolt uses syscalls for memory mapping that aren't available in
JS/WASM builds, we need to make sure we don't reference that code at
all. Otherwise we can't use parts of lnd as a library in projects that
are being compiled down to a WASM binary.

kvdb/backend.go

@@ -1,3 +1,5 @@
+// +build !js
+
 package kvdb
 
 import (