Fix powershell foxdump

[asantoma]

Describe your changes

I've tried the powershell foxdump module on a win10 x64 target with a recent firefox version and noticed it's not working so I've addressed the following issues:

• The script tried to import NSSBase64_DecodeBuffer from nss3.dll, which doesn't seem to export it anymore. I've replaced the usage of NSSBase64_DecodeBuffer with the powershell built-in FromBase64String;
• The script looked for the first Firefox profile whose name matched *.default but that profile may not exist or may not contain credentials. I've updated it to dynamically try to determine all profiles present in Mozilla\Firefox\Profiles\ and dump credentials from them;
• The script wouldn't start on an x64 bit machine because of a 64-bit check killswitch. I've removed it and instead made it search for a 64-bit firefox installation if it detects it's running as a 64-bit powershell process.
• The script would load two unused dlls: msvcp120.dll and msvcr120.dll. I've removed the loading of those DLLs since they are not needed and they are outdated (only msvcp140.dll exists on current firefox)

I have manually tested the script and its execution as an Empire module and I have found it to work.

Issue ticket number and link (if there is one)

Checklist before requesting a review

• I have performed a self-review of my code
• If it is a core feature, I have added thorough tests.
• I have added an entry to CHANGELOG.md
• I have updated the documentation in docs/ (if applicable)