Delete OldStyleClearD. (#14874)

Delete OldStyleClearD. (#14874)

* Delete OldStyleClearD from flowgraph

BlockSetOps::Assign requires sets to have the same size, there is no an
additional risk to use ClearD then.

* delete OldStyleClearD from regalloc

regalloc doesn't create new local variables and doesn't change epoch.

* Delete OldStyleClearD from copyprop

CopyProp doesn't create new vars.
Also `VarSetOps::Assign(this, compCurLife, block->bbLiveIn); ` before
the loop requires epoch to be the same.

* Delete OldStyleClearD from assertionpop

Assertion prop doesn't change epoch.

* Delete OldStyleClearD from the emmit

Because it doesn't create new local vars.

* Delete declarations