sysutils/ttyd: Only link with shared library

Due to how upstream handles libraries ttyd picks up both static and
shared library of libwebsockets which is not intended. The least
intrusive way I found is to simply detect it using pkgconfig instead.
While at it, disable check for git to determine version.

Reported by: Jeff Schmidt <jeff.jschmidt@gmail.com>
Approved by: portmgr (blanket, build fix)