Linode plans filter by planid, remove hack

While testing this, I found that `Fog::Compute::Linode` was incorrectly referenced in a couple places.

I was able to test as in: 
```
>> Fog::Compute.new(:provider=>'Linode').flavors.get 1
  <Fog::Compute::Linode::Flavor
    id=1,
    disk=24,
    name="Linode 1024",
    ram=1024,
    price=10.0
  >
```

But (even on fog/master) I get the full list when I try:
```
>> Fog::Compute.new(:provider=>'Linode').flavors :id=>1
```
Is this intended to return the specific flavor?