Docs: Rephrase `Public-Key-Pins` related info
Docs: Rephrase `Public-Key-Pins` related info

Rephrase part about `Public-Key-Pins` from `no-disallowed-headers.md`
so to reflect that the `Public-Key-Pins` header is the one creating
the problems, not `Public-Key-Pins-Report-Only`.

sonarwhal/sonar,alrra/sonar,alrra/sonar,sonarwhal/sonar,sonarwhal/sonar,alrra/sonar