perfparser complains about memfd-allocated files

For example:

PerfUnwind::ErrorCode(MissingElfFile): Could not find ELF file for /memfd:JSVMStack:/home/ulf/dev/qt5dev/qtbase/lib/libQt5Qml.so.5 (deleted). This can break stack unwinding and lead to missing symbols.

You cannot look up memfd-allocated files by name, so this is pointless. Also, reporting the file name of this path as the binary is pointless. We shouldn't report any file names for special regions.