Revert "[Folly] Helper method to get exception type"

Summary: This reverts commit 2c4f8da739ba0294f2c947753a0e30fee291feb5.

Test Plan: Compiles

Reviewed By: tudorb@fb.com

FB internal diff: D1108840

folly/String.h

@@ -352,13 +352,6 @@ inline size_t demangle(const std::type_info& type, char* buf, size_t bufSize) {
   return demangle(type.name(), buf, bufSize);
 }
 
-/**
- * Debug string for an exception: include type only.
- */
-inline fbstring exceptionTypeStr(const std::exception& e) {
-  return folly::to<fbstring>(demangle(typeid(e)));
-}
-
 /**
  * Debug string for an exception: include type and what().
  */