[Hackday][2.7] Added deprecated notes to '_method' and '_scheme' route requirements

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | no
| Fixed tickets | [#12641, #12640]
| License       | MIT
| Doc PR        |
sorry i didn't want to confuse you.  what do you think about:

     trigger_error('The router "_method" ...)
     trigger_error('The router "_scheme" ...)

i changed:
using " instad of \'
throwing a message for _method and _scheme. i think it's worth because it's much more maintainable.