Remove google test submodule

It had been added for some strange reason, allthough it's supposed
to be there only in another branch.

diff --git a/lib/googletest b/lib/googletest
deleted file mode 160000 (submodule)
index ec44c6c..0000000
--- a/lib/googletest
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit ec44c6c1675c25b9827aacd08c02433cccde7780