libc: Move ssize_t definition to sys/types.h

There's no need to have a separate file for this, and we'll be adding
other types like off_t here soon as well.

Change-Id: I40629a5a0fba7af44828eaeead294e4e55844bb0
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
2 files changed