Remove Late Cancel contract to make TileLink implementation compatible with spec.

[sequencer]

The valid-cancel decoupling strategy is never used in public open source projects, including sifive-inclusive-cache, sifive-blocks, chipyard and Xiangshan. This is basically an untested, off-spec, non-open-source used feature, which introduce maintaining complexity for current rocket-chip maintaining procedure. Thus I propose removing this for exactly aligning the TileLink implementation to the spec, which makes unittest easier to go though. In the future, if there are any updates for TileLink spec, including but not limited to adding another decoupling protocol. New features will be added to rocket-chip(or related splitted projects) based on the TileLlink spec.

Related issue: #2480

Type of change: other enhancement

Impact: API modification

Development Phase: implementation

Release Notes Remove Valid-Cancel decoupling in TileLink

[michael-etzkorn]

As far as I've gathered while combing through PRs for versioning, this was an experimental off-spec idea for fixing timing paths.

https://github.com/chipsalliance/rocket-chip/pull/2480