Get rid of `EmgCannon`, `Flamer` and `DGun` weapon types

[sprunk]

Figure out what it does that Cannon or LaserCannon don't. Add that functionality (if any) to Cannon or LaserCannon, then remove.

[IcarusRTS]

In order for this to be accomplished. the FireImpl function needs to check what type of weapon is it before executing the code as each one's function executes a different set of code and make Init function execute when the weapon is DGun specifically.