profiling: attempt to remove per-cpu profile flip bufferHEADmaster

This is the really old legacy kernel profiling code, which has long
since been obviated by "real profiling" (ie 'prof' and company), and
mainly remains as a source of syzbot reports.

There are anecdotal reports that people still use it for boot-time
profiling, but it's unlikely that such use would care about the old NUMA
optimizations in this code from 2004 (commit ad02973d42: "profile: 512x
Altix timer interrupt livelock fix" in the BK import archive at [1])

So in order to head off future syzbot reports, let's try to simplify
this code and get rid of the per-cpu profile buffers that are quite a
large portion of the complexity footprint of this thing (including CPU
hotplug callbacks etc).

It's unlikely anybody will actually notice, or possibly, as Thomas put
it: "Only people who indulge in nostalgia will notice :)".

That said, if it turns out that this code is actually actively used by
somebody, we can always revert this removal.  Thus the "attempt" in the
summary line.

[ Note: in a small nod to "the profiling code can cause NUMA problems",
  this also removes the "increment the last entry in the profiling array
  on any unknown hits" logic. That would account any program counter in
  a module to that single counter location, and might exacerbate any
  NUMA cacheline bouncing issues ]

Link: https://lore.kernel.org/all/CAHk-=wgs52BxT4Zjmjz8aNvHWKxf5_ThBY4bYL1Y6CTaNL2dTw@mail.gmail.com/
Link:  https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git [1]
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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