TOOL_SIMILARITY in fuse.py

Reported by a user:

The python script tools/fuse.py seems to use a path that does not exist. The error is the following:

! failed: ../algo/tools/similarity

The cause is the following variable / the broken link in ../algo/tools -> ./tools/:

TOOL_SIMILARITY = "../algo/tools/similarity"

It works without the error massage when switching to the following line:

TOOL_SIMILARITY = "./similarity.cgi

The algo path does not exist in releases (contrary to the git). The error does not stop fuse.py, but we should perhaps remove that or put this under an option. see #1990 #3019