Simplify modifyLiquidity

[jeffishjeff]

Description of changes

• It's not necessary to initialize feeGrowthOutside (and by extension feeGrowthInside) for newly initialized ticks, as feeGrowthInside is always taken in relativity when used for calculating feeOwned
• If that's removed, we can move fee accrue logic to the front in modifyLiquidity(), then combine previously fragmented tick related logic (i.e. clear tick) all inside updateTick()
• Net result is a bit of gas saving and making the code easier to read

[hensha256]

Hi! Thanks so much for your contribution. Given the code has already completed 5 audits, we are not going to be making any new changes other than in the event that a bug is found.