Maybe remove the not necessary `runtime.KeepAlive()`

According to this discussion https://forum.golangbridge.org/t/curious-about-runtime-keepalive-usage/3530, some common scenarios that need to call `runtime.KeepAlive()` is
1. you have obtained the file descriptor to an underlying os.File.
2. you have passed memory to cgo which was allocated inside the same function.

In wasmtime-go, the variable that we are calling `runtime.KeepAlive()` for are normally not allocated by the same function, so I think maybe we don't need `runtime.KeepAlive()`?