Remove unused variable in catch(...) expressions

Summary:
D17629896 was intended to fix this in ovrsource, but it turns out these changes should be made on fbsource first then get synced.

The MSVC build of OculusPCSDK has numerous warnings, including these low-hanging fruit:

```
c:\open\ovrsource\xplat\omnistore\client\common\reportsubscriptionstatetiming.cpp(28): warning C4101: 'e': unreferenced local variable
c:\open\ovrsource\xplat\omnistore\client\common\databaseanalyticsmetadatatiming.cpp(23): warning C4101: 'e': unreferenced local variable
c:\open\ovrsource\xplat\omnistore\client\common\sendqueuereportbacklogtiming.cpp(32): warning C4101: 'e': unreferenced local variable
c:\open\ovrsource\xplat\omnistore\client\common\omnistore.cpp(192): warning C4101: 'e': unreferenced local variable
c:\open\ovrsource\xplat\omnistore\client\common\omnistore.cpp(907): warning C4101: 'e': unreferenced local variable
c:\open\ovrsource\xplat\omnistore\client\common\omnistore.cpp(934): warning C4101: 'e': unreferenced local variable
c:\open\ovrsource\xplat\omnistore\client\common\omnistore.cpp(946): warning C4101: 'e': unreferenced local variable
```

Clang doesn't complain, but the code is just as clear without the 'e' so best to remove.

Reviewed By: vener91

Differential Revision: D17631747

fbshipit-source-id: 0190a48e640311b40c9d1b988b0c07cfbdcfd7e5

xplat/Flipper/ConnectionContextStore.cpp

@@ -85,7 +85,7 @@ std::string ConnectionContextStore::getDeviceId() {
     auto maybeDeviceId = folly::parseJson(config)["deviceId"];
     return maybeDeviceId.isString() ? maybeDeviceId.getString()
                                     : deviceData_.deviceId;
-  } catch (std::exception& e) {
+  } catch (std::exception&) {
     return deviceData_.deviceId;
   }
 }