Fix CMake script for static, auto-download, cln configuration (#7957)

Fix CMake script for static, auto-download, cln configuration (#7957)

The script was previously creating a 'CLN_STATIC_LIBRARIES' variable that
wasn't known about elsewhere in the code and caused issues when the Makefiles
depended on a CLN_LIBRARIES variable. Instead, the static libraries should just
go into CLN_LIBRARIES as normal.

This only seems to have affected the case where cln is set to auto-download and
the build is static.

Signed-off-by: Matthew Sotoudeh sotoudeh@stanford.edu