Get rid of 2 unnecessary ASTSimplifier rules
Get rid of 2 unnecessary ASTSimplifier rules

Those rules were:

```
if (cond) { A; unreachable} B;`
becomes `if (cond) { A; unreachable; } else { B }

if (cond) { A; } else { B; unreachable }  C;`
becomes `if (cond) { A; C; } else { unreachable }
```

Due to improvements in the way Phan merges variables from different
branches, these rules are now unnecessary workarounds.

etsy/phan,etsy/phan