hpcprof: use pretty_name as the key to unify vmlinux files
hpcprof: use pretty_name as the key to unify vmlinux files

We want to merge all vmlinux.aaaa, vmlinux.bbbb, ... into a single vmlinux.
Using ::pretty_name() will return "<vmlinux>" instead of the original name "<vmlinux.aaaaa>"
This will automatically merge all <vmlinux.xxxx> files in the flat view.

HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit