internal/godoc/dochtml/internal/render: don't use safetemplate alias
internal/godoc/dochtml/internal/render: don't use safetemplate alias

github.com/google/safehtml/template no longer uses the safetemplate
alias in internal/godoc/dochtml/internal/render/linkify.go for
consistency in the package, and because it isn't necessary.

Change-Id: I4604c09fd6dca9d804187f395127233e7ed4c4f9
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/261141
Trust: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>
Run-TryBot: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>
TryBot-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite