Remove @forceInline from the inlining doc

[japgolly]

According to https://dotty.epfl.ch/docs/reference/metaprogramming/inline.html,

To cross compile between both Scala 3 and Scala 2, we introduce a new @forceInline
annotation which is equivalent to the new inline modifier. Note that
Scala 2 ignores the @forceInline annotation, so one must use both
annotations to guarantee inlining for Scala 3 and at the same time hint inlining
for Scala 2 (i.e. @forceInline @inline).

but it seems that @forceInline was removed in #7475. The documentation should be updated.

Note: I don't know what the replacement solution for cross-compilation is so if someone could share that'd be awesome.

[japgolly]

Sorry @nicolasstucki so just to confirm, there's no replacement for this? There's still only @inline which Scala 3 will treat the way Scala 2 does?