buildhistory: Fix srcrevs output

The code was assuming that the a recipe with only one srcrev wouldn't "name"
it. This isn't the case as the glibc or bzip2 recipes show, you can have
a single srcrev which is named.

We can pull the data from the fetcher and in fact we already have it, we just
need to handle the "default" case and make that code the default for all srcrev
regardless of length.

[YOCTO #14017]

(From OE-Core rev: 45ae567932ba52b758eb41754453e9828d9533a1)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>