A RAM heatsink or RAM cooler is an accessory that is designed to remove excess warmth from the memory modules inside of your computer. A typical RAM heatsink consists of multiple metal fins connected to a base plate which acts as a radiator. These cool the RAM by transferring the excessive heat into a liquid or other medium to maintain the desired temperature of the RAM.
Unlike the CPU which has many more transistors, RAM has very few, making it much less likely to overheat. However, if it does overheat for any reason it can be susceptible to thermal throttling which will cause the device to slow down drastically until the heat dissipates. This can damage the chip and shorten its lifespan, so it is a good idea to keep your RAM cool.
That said, a RAM heatsink/heat spreader is still useful if you plan on overclocking your RAM to higher than stock speeds. It helps with keeping the temperature down when you put the RAM through stressful usage scenarios, but it is not necessary for most use cases or even a majority of PC users.
The bottom line is that RAM doesn’t make enough heat to need a heat sink, even without one it will only get hotter by a few degrees on average. Trying to take the heatsinks off of your RAM is not advised as it will most likely ruin them, since they are normally glued to the dimm with some form of thermal compound (or straight glue in some cases). If you really want to try and remove the heatsinks from your RAM stick I would recommend doing so very carefully using a hairdryer or heat gun.