You need Some Form of chain tension adjustment
either horizontal dropouts -you dont have them
a dedicated chain tensioner -you dont want to spend money
a rear derailer used as a tensioner -go for it!

going the route of 'the chain is just the right length if I take out these links' doesn't work long term. Because chains wear down and get longer (pivots get looser) over time and then it's no longer the right length anymore.

so between constantly buying new chains, $$$ in the long run
or spending on a chain tensioner $ or modified derailer now
a tensioner/derailer is cheaper