Hardcopy of pybind11 instead of using git submodules (#552)

* removed pybind as submodule
* added hardcopy of pybind11 2.10.0
* rename pybind11 folder to avoid conflicts when changing branch

Co-authored-by: Dhanya Thattil <dhanya.thattil@psi.ch>

libs/pybind/tests/test_cmake_build/main.cpp

@@ -0,0 +1,6 @@
+#include <pybind11/pybind11.h>
+namespace py = pybind11;
+
+PYBIND11_MODULE(test_cmake_build, m) {
+    m.def("add", [](int i, int j) { return i + j; });
+}