Remove traceImportant from build.template file in the successful generateHelp branch

[prosconi]

In the generateHelp method in the build.template file

https://github.com/fsprojects/ProjectScaffold/blob/master/build.template#L185

let generateHelp fail =
    if executeFSIWithArgs "docs/tools" "generate.fsx" ["--define:RELEASE"; "--define:HELP"] [] then
        traceImportant "Help generated"
    else
        if fail then
            failwith "generating help documentation failed"
        else
            traceImportant "generating help documentation failed"

traceImportant writes to standard error and can cause some build systems to fail because of this. Recommend using trace instead.