Remove unused exception parameter from openr/decision/LinkState.cpp

Summary:
`-Wunused-exception-parameter` has identified an unused exception parameter. This diff removes it.

This:
```
try {
    ...
} catch (exception& e) {
    // no use of e
}
```
should instead be written as
```
} catch (exception&) {
```

If the code compiles, this is safe to land.

Reviewed By: xiangxu1121

Differential Revision: D52957711

fbshipit-source-id: a831a9e4e1b8a296f85e59917da8d8a797adadab

openr/decision/LinkState.cpp

@@ -274,7 +274,7 @@ LinkState::removeNode(const std::string& nodeName) {
     try {
       CHECK(linkMap_.at(link->getOtherNodeName(nodeName)).erase(link));
       CHECK(allLinks_.erase(link));
-    } catch (std::out_of_range const& e) {
+    } catch (std::out_of_range const&) {
       XLOG(FATAL) << "std::out_of_range for " << nodeName;
     }
   }