remove OverwritingHeader

[jnfoster]

Per 4/24 LDWG discussion.

[mihaibudiu]

This is more subtle:

• if P4-14 requires this error we have to insert a check in the compiler when compiling extracts
• if BMv2 triggers this error automatically, we have to invalidate headers prior to extraction
  @antoninbas : what is the right way to handle this to remain compatible with P4-14 and to provide the right semantics for P4-16?

[antoninbas]

I don't think there is anything in the p4_14 spec that says you cannot extract to the same header twice, so I think you are fine on that side.
I have a pull request opened to stop triggering this error in bmv2 (p4lang/behavioral-model#358). I think I should be good to merge it even before you make the compiler change, but just in case I'll wait until you have a PR ready.

[mihaibudiu]

@antoninbas : does bmv2 still trigger this error?

[antoninbas]

Not if I merge this: p4lang/behavioral-model#358

[antoninbas]

So @mbudiu-vmw can I merge the bmv2 pull request to stop triggering the error?

[mihaibudiu]

I think that it is safe to do so.