Drop useless network/syslog_basic.phpt (#8526)

This test asserts that `syslog()` returns true, but that is the case
anyway[1].  Since there is already misc/syslog_basic.phpt, the test has
no further raison d'être.

[1] <https://github.com/php/php-src/blob/d4e24e72afc269f392eabd74abeb6ea86894740d/ext/standard/basic_functions.stub.php#L697-L698>

Author: cmb69