Don't build the static libgit2

This keeps sneaking in when merging from 'next'.
diff --git a/Makefile b/Makefile
index 39fc558..fa6964f 100644
--- a/Makefile
+++ b/Makefile
@@ -1,9 +1,6 @@
 default: test
 
-build-libgit2:
-	./script/build-libgit2-static.sh
-
-test: build-libgit2
+test:
 	go run script/check-MakeGitError-thread-lock.go
 	go test ./...