Remove StackTraceSimplifier

Related issue: #2735

Motivation:

When an application is under load and experiencing a lot of failure, the
instantiation of DefaultExceptionEvent spends noticeable amount of time
because of StackTraceSimplifier.

Also, StackTraceSimplifier makes people sometimes confused because it
hides the execution path partially.

Modifications:

Remove the use of StackTraceSimplifier

Result:

JVM spends much less time at Throwable.getStackTrace()