ports/75117: update port: net/boinc-client - Makefile/plist correction
for when package is used
Correction to the Makefile and pkg-plist to ensure proper
creation and removal of the ${PREFIX}/boinc/projects directory
when port is installed from a pre-compiled package.
PR: ports/75117
Submitted by: "J.R. Oldroyd" <fbsd@opal.com>