NetworkPkg/TlsAuthConfigDxe: replace OpenFileByDevicePath() with UefiLib API
    
    Replace the OpenFileByDevicePath() function with EfiOpenFileByDevicePath()
    from UefiLib, correcting the following issues:
    
    - imprecise comments on OpenFileByDevicePath(),
    - code duplication between this module and other modules,
    - local variable name "EfiSimpleFileSystemProtocol" starting with "Efi"
      prefix,
    - bogus "FileHandle = NULL" assignments,
    - passing a potentially unaligned "FILEPATH_DEVICE_PATH.PathName" field to
      a protocol member function (forbidden by the UEFI spec),
    - leaking "Handle1" when the device path type/subtype check fails in the
      loop,
    - stale SHELL_FILE_HANDLE reference in a comment.
    
    Cc: Jiaxin Wu <jiaxin.wu@intel.com>
    Cc: Siyuan Fu <siyuan.fu@intel.com>
    Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1008
    Contributed-under: TianoCore Contribution Agreement 1.1
    Signed-off-by: Laszlo Ersek <lersek@redhat.com>
    Reviewed-by: Jiaxin Wu <jiaxin.wu@intel.com>
    Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>