Fix version check

[Mapioe]

There was a logical bug in pkg/version/version.go that did an early return from a function that extracted installed versions; only the --version flag was checked. My changes propose to completely remove the second flag (version) to keep consistency across all PD tools. Also fixed the error message that was hard-coded and confusing.

Before

❯ pdtm
skip
23. tunnelx (not installed)
24. uncover (latest) (1.2.1)
25. urlfinder (not installed)
26. vulnx (not installed)
❯ vulnx version
[INF] Current vulnx version 2.0.1 (latest)
❯ tunnelx --help
A socks5 proxy server that tunnels traffic through a remote server
❯ urlfinder
fish: Unknown command: urlfinder

After

❯ ./pdtm
skip
23. tunnelx (exit status 2)
24. uncover (latest) (1.2.1)
25. urlfinder (not installed)
26. vulnx (exit status 1)

vulnx and tunnelx will throw an error even when installed because they do not currently use the --version flag. It is already fixed in the latest git commit of tunnelx but not in the build release. Below is latest tunnelx builded myself and placed into .pdtm/go/bin

snip
23. tunnelx (latest) (0.0.1)

This shouldn't happen in the future as all new applications should be advised to implement --version flag.
Kinda reverts #423