Kill the libreofficekit static library / shim.c.

It looks like the cleanest method of getting lok_init into
a LibreOfficeKitInit.h header (in a c89 compatible way) is to
have it as a static function.

(inline is only available in C99 or later -- this is actually
 available on Linux which is the only place that we can actually
 use lok_init anyways currently, however given we have to keep
 c89 for the C code (for MSVC) compatibility, selectively enabling
 c99 would likely be more messy.)

Change-Id: I0493e7a68ed5397479220bb6ba8c3db870b6dd32