removed dup of _global.scss refactored with new style em-calc call

I was getting an error when uncommenting line 844 when using compass:
```
$orbit-bullet-radius: emCalc(18);
```

but changing it to

```
$orbit-bullet-radius: emCalc(18px);
```
resolved the issue.

Upon investigating further I noticed that there are duplicated and different versions of emCalc that caused the error. I removed this duplicate and incorrect code and refactored all references to `emCalc()` to the newer style `em-calc()`