content/static: remove icon next to source files
content/static: remove icon next to source files

Removes icons from source files and adjusts
spacing of the grid for better readability.

Change-Id: I7ef7c8fc19dd641652219321f113862277be0830
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/260728
Trust: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Run-TryBot: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
TryBot-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>

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