www/grafana8: remove duplicates from distinfo

The Azure go-autorest project (https://github.com/Azure/go-autorest)
provides several go modules within the same tarball, but the Grafana
code requires different commits for several of those modules, hence
the same source appearing multiple times at different commmit hashes
in distinfo.

Unfortunately, with grafana 8.3.3, three of the go-autorest modules
required the same commit hash, leading to duplication in the distinfo.
This causes a problem when trying to download the distfiles the first
time -- a number of the downloads will fail. Repeatedly attempting to
download will succeed for one more of the various different versions
of the go-autorest distfile, until eventually everything has been
successfully downloaded.

Remove the duplicate items in distinfo so that first-time download
into a virgin distfiles directory does succeed. This means that the
result of make makesum cannot be used un-edited.

PR: 260537
Reported by: John D.

(cherry picked from commit dcd67527ab526dcb8683565796f1ac2e8b6bc6a7)