Unnecessary stack checks and prologue for wasm functions containing a single `return_call_ref`

Given this input:

```wasm
(module
(type $t (func))
(global (export "g") (mut (ref $t)) (ref.func $f))
(func $f)

(func (export "call")
(return_call_ref $t (global.get 0))
)
)
```

this currently compiles as:

```
$ wasmtime compile foo.wat
$ wasmtime objdump foo.cwasm --filter 1
wasm[0]::function[1]:
pushq %rbp
movq %rsp, %rbp
movq 8(%rdi), %r10
movq 0x18(%r10), %r10
addq $0x10, %r10
cmpq %rsp, %r10
ja 0x52
movq 0x30(%rdi), %rsi
movq %rdi, %r8
movq 8(%rsi), %r10
╰─╼ trap: Normal(NullReference)
movq 0x18(%rsi), %rdi
movq %r8, %rsi
movq %rbp, %rsp
popq %rbp
jmpq *%r10
ud2
╰─╼ trap: Normal(StackOverflow)
```

There's a few inefficiencies with this codegen we could improve upon:

* There's an explicit stack check as `cmpq %rsp, %r10` here which isn't necessary. That's injected for functions in general which call another function, but it's not injected for leaf functions, and in this case this is sort of a leaf function.
* This sets up a prologue/epilogue which isn't necessary for this "mostly leaf" function.
* There's a trap registered for a null function reference, but this function reference type can't be null so that's not necessary.

Nothing major here, but might be nice to clean up some of this as well.