sdjournal: drop conditional static specifier
sdjournal: drop conditional static specifier

`_SD_ARRAY_STATIC` is a custom / conditional macro for static C99
array size, which got introduced in recent libsystemd and thus cannot
build on older versions.
Due to how it is currently used in our Go wrapper, it can be safely
omitted from here.

Ref: https://github.com/systemd/systemd/commit/4199f6896aee4394bddfb85e45eabe34d60038cb

coreos/go-systemd,coreos/go-systemd