Fix google font specifying all font options

[kylebutts]

Just a small thing. Here, you specify which font variants and weights to load. This causes error with pagedown::chrome_print because not every google font has every option. Fortunately, you don't need to specify any and it will load them all. So I think it's better to just delete that part of the line

https://github.com/rstudio/gt/blob/df86e0cf76ac5eaa6732ca567ea9a9b3cfdc2f7d/R/helpers.R#L2237

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