2003 -- review porting notes

Stream: mathlib4

[Johan Commelin]

@porters Now that 2003 is in core, we should review a whole lot of porting notes about timeouts. There are 3 explicit mentions of 2003 in porting notes:

Mathlib/Algebra/Star/SelfAdjoint.lean
369:-- Porting note: This takes too long. lean#2003?

Mathlib/Algebra/DirectSum/Basic.lean
393:-- Porting note: This times out; lean4#2003 may fix this?

Mathlib/Data/Sign.lean
95:-- Porting note: This takes too long, likely fixed by lean4#2003

but there are probably a lot of other places that should be reviewed.