Cleanup fs_getline from fs_mgr

Since getline is included in bionic, fs_mgr can use this version instead of
the one defined internally by fs_getline.

Replace fs_getline with getline.

Change-Id: I49b53d639bd995f051256fb7573ff6ab45d9c36d
Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>