Modules: Clean up ModuleFile::Imports in ModuleManager::removeModules

I don't have a testcase for this (and I'm not sure if it's an observable
bug), but it seems obviously wrong that ModuleManager::removeModules is
failing to clean up deleted modules from ModuleFile::Imports.  See the
code in ModuleManager::addModule that inserts into ModuleFile::Imports;
we need the inverse operation.

llvm-svn: 293399
diff --git a/clang/lib/Serialization/ModuleManager.cpp b/clang/lib/Serialization/ModuleManager.cpp
index 358dd0e..609eedf 100644
--- a/clang/lib/Serialization/ModuleManager.cpp
+++ b/clang/lib/Serialization/ModuleManager.cpp
@@ -204,10 +204,10 @@
     return victimSet.count(MF);
   };
   // Remove any references to the now-destroyed modules.
-  //
-  // FIXME: this should probably clean up Imports as well.
-  for (auto I = begin(); I != First; ++I)
+  for (auto I = begin(); I != First; ++I) {
+    I->Imports.remove_if(IsVictim);
     I->ImportedBy.remove_if(IsVictim);
+  }
   Roots.erase(std::remove_if(Roots.begin(), Roots.end(), IsVictim),
               Roots.end());