Revert #102 PhantomJS `version = "auto"` logic for windows

[schloerke]

Related: https://github.com/wch/webshot/pull/102/files Related: https://github.com/rstudio/fontawesome/pull/61

• Kept the logic within is_phantomjs_version_latest() to help trim up the trailing "beta" or "development" in the version.