Refactor ga_init()

`garray.c` contains both `ga_init()` and `ga_init2()`. `ga_init()`  is used exactly once outside of `garray.c`. On the other hand, `ga_init2()` is used around 80 times throughout the code base. There is no need to have both of these functions, so this PR inlines `ga_init()` and renames `ga_init2()` to `ga_init()`.