build: use 'git submodule deinit' instead of 'rm -rf'

build: use 'git submodule deinit' instead of 'rm -rf'

Fix submodule handling: deinit submodules instead of
removing them and call update with --recursive, needed
to checkout gtest within gmock.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>