delete version gives confusing errors if the crate wasn't a library

[jyn514]

What it says:

Error: failed to delete the crate

Caused by:
    <?xml version="1.0" encoding="UTF-8"?>
<Error><Code>MalformedXML</Code><Message>The XML you provided was not well-formed or did not validate against our published schema</Message><RequestId>9F280BB6EBFEC7F3</RequestId><HostId>sgrbwS6rXn83txaNR4V3+YyVm/+VhIrD1Nhaiv9og8H5hNnGq2yntXaGt45DQ8rcmopLRGoPqkg=</HostId></Error>

What it should say: nothing, just don't reach out to s3 in the first place.

This is low priority because deleting the crate from the database still works fine.

As a secondary issue, delete version should probably not delete the crate from the database unless deleting the s3 documentation succeeds.