Fixes and minor clean ups for tracing:

 - Fix memory leak by reverting what was thought to be a double free.
   A static tool had gave a false positive that a double free was
   possible in the error path, but it was actually a different location
   that confused the static analyzer (and those of us that reviewed it).

 - Move use of static buffers by ftrace_dump() to a location that can
   be used by kgdb's ftdump(), as it needs it for the same reasons.

 - Clarify in the Kconfig description that function tracing has negligible
   impact on x86, but may have a bit bigger impact on other architectures.

 - Remove unnecessary extra semicolon in trace event.

 - Make a local variable static that is used in the fprobes sample

 - Use KSYM_NAME_LEN for length of function in kprobe sample and get
   rid of unneeded macro for the same purpose.
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