Installing floor threshold/transition - should I remove existing grout between wood laminate and ceramic tile?
I would advise you to remove all that old grout.  Give the laminate room to expand and contract.  When you put the new transition piece in, if possible to make it secure by only glueing it on the tile, that would be best. If that doesn't seem to hold it secure enough,  glue to the tile and use a caulk that stays flexible on the laminate side. That laminate wants to move in temp and humidity changes.