No need to define ETIME

No need to define ETIME

(which is an obsolescent XSI-STREAMS Posix extension).  It's only use is in the
big switch in UnixErrnoString in sal/osl/unx/uunxapi.cxx, so if any platform
should actually lack it, we should rather #ifdef its use there than introduce it
here.

(This started to cause

> sal/osl/unx/system.hxx:190:12: error: macro 'ETIME' has been marked as deprecated: ETIME is deprecated in ISO C++ [-Werror,-Wdeprecated-pragma]
>   190 | #   ifndef ETIME
>       |            ^
> ~/llvm/inst/bin/../include/c++/v1/cerrno:51:67: note: macro marked 'deprecated' here
>    51 | #  pragma clang deprecated(ETIME, "ETIME is deprecated in ISO C++")
>       |                                                                   ^

with recent LLVM 19 trunk on macOS now.)

Change-Id: I01a586f08a4d9e4643c797fce5ce53c5f3ce8b81
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/165303
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <stephan.bergmann@allotropia.de>