internal/frontend: move version type metric variables
internal/frontend: move version type metric variables

Variables related to version type are moved to the bottom of the page,
closer to recordVersionTypeMetric which is the relevant function. Pure
code in motion.

Change-Id: I97332364cb65acba96455fa2293bb97c43d98857
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/270577
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