x/pkgsite: remove protocol from source code links

[Stexxe]

A new template function for stripping scheme from URL applied to repository
URL in the Details block.

Fixes golang/go#40943

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This PR (HEAD: 5d5902d) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/pkgsite/+/310229 to see it.

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Patch Set 1:

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Message from Jonathan Amsterdam:

Patch Set 1: Code-Review+1

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Message from Jonathan Amsterdam:

Patch Set 1:

(1 comment)

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This PR (HEAD: a2b0ca2) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/pkgsite/+/310229 to see it.

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See the Wiki page for more info

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Message from Aleksei Tirman:

Patch Set 2:

(1 comment)

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Message from Jamal Carvalho:

Patch Set 2: Trust+1

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This PR is being closed because golang.org/cl/310229 has been merged.