Make FSUIPC optional

Summary:
If FSUIPC is configured, its support will be enabled in swift
and disabled otherwise.

Ref T91

Reviewers: #swift_pilot_client, msutcliffe

Reviewed By: #swift_pilot_client, msutcliffe

Subscribers: msutcliffe, jenkins, kbasan

Maniphest Tasks: T91

Differential Revision: https://dev.swift-project.org/D28

mkspecs/features/libraries.pri

@@ -32,13 +32,6 @@ blackcore {
     }
 
     LIBS *= -lblackcore -lvatlib
-
-    win32 {
-        contains(BLACK_CONFIG, FSX) {
-            LIBS *= -lSimConnect
-            LIBS *= -lFSUIPC_User
-        }
-    }
 }
 
 blacksound {