tr replaces character by character. If you want to replace _all_ = with blanks you could use

tr/=/ /;
[download]

If you want to delete them you use

tr/=//d;
[download]

If you want to delete last = in a string you could do it with s/// instead like in

s/=\s*$//;
[download]

that matches a = followed by nothing or whitespace and replaces it with nothing. /t0mas