tree-wide: replace "asked to inhibit it" with "is inhibiting this"

tree-wide: replace "asked to inhibit it" with "is inhibiting this"

The problem with the original form is that the subject of the sentence with
passive void is "the system", and we're not inhibiting the system. In English
the sense can be made out, but the form is gramatically incorrect.
In fact, the Polish translation got this wrong:
> msgid "Power off the system while an application is inhibiting this"
> msgstr "Wyłączenie systemu, kiedy program zażądał jego wstrzymania"
"jego" can only refer to "the system", because of gender mismatch with "power
off". If our translators cannot grok the message, then we should probably reword
it.

Also, drop the "asked to" part. Everything we do is over IPC, so we only ever
"ask" for things, and this adds no value.