Update messages.h

[zaydogan]

via pr 59641
message: ">: installed package has a greater version than available package" is misleading, because it implies that the package is installed, where in reality it is not installed, but a newer version is available. Changing the message to "package is not installed and a greater version is available" is more understandable and avoids confusion. Credits: Van Ly

[jperkin]

To be honest I don't like either wording.

The important thing to note here is that the packages are not the same thing. They might have the same PKGBASE but as they have different PKGPATH then pkgin treats them as fundamentally different.

In my opinion it's reasonable to show these marks for a matching PKGPATH as it's helpful to show what the current state of the package is compared to the remote repository, but conflating that with fundamentally different packages only results in the confusion that is apparent with this bug report.

This needs more work to first ensure that if the package does not match PKGPATH then none of these marks should be shown at all, and then improve the message accordingly.