No, no, and no. I'm interested to see what some of the more experienced container growing members here have to say but to my eye, that sucker looks well above the graft line, seen in your last picture just above bark level. If you want more of a trunked tree verses a bush, then prune it off but if you don't mind having a bushy lemon tree, it's just more branching structure.

If the leaves are healthy, they are contributing photosynthesis. Keep em.

And finally, that pot looks plenty big.

I agree with fireball. Watering twice a week may be too frequent.

Check to see if it needs water by digging
a couple of inches into the soil mix to see if it is damp. Alternatively, shove
a wooden skewer halfway between the tree and the wall of the pot and all the
way to the bottom. Pull it out and if you see particles on it, then it does not
need watering.