replace go-bls-sigs and go-sectorbuilder with filecoin-ffi

- remove old submodules and add new submodule
- update build tooling to consume new unified static library
- update consumers of old libs to use new package

.gitmodules

@@ -1,6 +1,4 @@
-[submodule "extern/go-bls-sigs"]
-	path = extern/go-bls-sigs
-	url = https://github.com/filecoin-project/go-bls-sigs.git
-[submodule "extern/go-sectorbuilder"]
-	path = extern/go-sectorbuilder
-	url = https://github.com/filecoin-project/go-sectorbuilder
+[submodule "extern/filecoin-ffi"]
+	path = extern/filecoin-ffi
+	url = git@github.com:filecoin-project/filecoin-ffi
+	branch = master