Option prefix should not be included in the freemarker map

[cmnbroad]

Historically the docgen code (going back to gatk3) included the option prefix ("--") as part of the argument name when populating the freemarker map. This was somewhat convenient when generating doc, but is increasingly awkward for things like WDL generation. This should be changed, and all the corresponding templates (here and in downstream projects) should be changed to use the names directly without the prefix.