Chains have two styles of links on them, inners and outers. Both are counted when determining total link length but you can't remove just one at a time, you must remove two. So, you couldn't make a 105 link length, you'd have to go 106. The master link is an outer link style. Both ends of the chain must end with an inner link so the master link (outer style) can join them together. When shortening a chain, you start with an inner. To get to the next inner, you have to remove that 1st inner plus an outer, or two links.
When shortening a chain, grind the riveted heads off the pins on the outer plate you plan on removing, then just pry the plate off and/or tap the ground off pins through it .....
Even if you have a chain breaker tool, it's still best to grind the riveted ends off the pins you plan on removing. It puts far less strain on the chain breaking tool. To determine the length needed, you could count the links but I never do that. I just string the chain on and pull it as tight as it will go. There's no chance of miscounting and getting the length wrong that way.
Since you must remove 2 links at a time, the couple tooth changes we usually make aren't enough to make shortening possible. A 32, 33, and 34T sprocket will all use the same 104 link length.