Revert "tracing: Constify string literal data member in struct trace_event_call"

This reverts commit c5a28af7 which is
commit 452f4b31 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I458b8264fccdb3f99eaf116e9babcaea50e405b3
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>