Schema: reword task input help string

[MetRonnie]

This is misleading:

It doesn't have to be a glob, and if it isn't a glob, then it will match inactive tasks as well as active ones.

https://github.com/cylc/cylc-flow/blob/4b58a6a7f53f69789466ac88b57832b1433b1679/cylc/flow/network/schema.py#L1597-L1601