[CaptureTracking] Avoid duplicate shouldExplode() check (NFCI)

We check shouldExplore() before adding uses to the worklist, so
uses that should not be explored will not reach captured() in the
first place.

llvm/lib/Analysis/CaptureTracking.cpp

@@ -159,9 +159,6 @@ namespace {
       if (isa<ReturnInst>(U->getUser()) && !ReturnCaptures)
         return false;
 
-      if (!shouldExplore(U))
-        return false;
-
       Captured = true;
       return true;
     }