cut catch-all exceptionStr overload

Summary: There are no correct uses of the catch-all overload of `folly::exceptionStr`. Every use is a bug of some kind, leading to the impression that this overload ought to be removed.

Differential Revision: D26539622

fbshipit-source-id: dc2ca0781ea02f1327a334bb1fe2e533fa46d1b3

folly/ExceptionString.cpp

@@ -20,6 +20,7 @@
 
 #include <folly/CPortability.h>
 #include <folly/CppAttributes.h>
+#include <folly/Demangle.h>
 #include <folly/functional/Invoke.h>
 #include <folly/lang/Exception.h>
 

folly/ExceptionString.h

@@ -17,13 +17,8 @@
 #pragma once
 
 #include <exception>
-#include <string>
-#include <type_traits>
-#include <typeinfo>
 
-#include <folly/Demangle.h>
 #include <folly/FBString.h>
-#include <folly/Portability.h>
 
 namespace folly {
 
@@ -35,15 +30,4 @@ fbstring exceptionStr(const std::exception& e);
 
 fbstring exceptionStr(std::exception_ptr ep);
 
-template <typename E>
-auto exceptionStr(const E& e) -> typename std::
-    enable_if<!std::is_base_of<std::exception, E>::value, fbstring>::type {
-#if FOLLY_HAS_RTTI
-  return demangle(typeid(e));
-#else
-  (void)e;
-  return "Exception (no RTTI available)";
-#endif
-}
-
 } // namespace folly