Remove incorrect power-user help text that only image sources are supported

[tomerse-sg]

What happened:
when I run syft power-user --help I see the below message:

it is specified that dir is not supported which is not true
What you expected to happen:
remove this message
Steps to reproduce the issue:
run syft power-user
Anything else we need to know?:

Environment:

• Output of syft version: 0.84.1
• OS (e.g: cat /etc/os-release or similar): macOS

[kzantow]

NOTE: this is in the help text.