perf tools: Fixup minor doc formatting issues

Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-annotate.txt

 perf-annotate(1)
-==============
+================
 
 NAME
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tools/perf/Documentation/perf-bench.txt

 perf-bench(1)
-============
+=============
 
 NAME
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tools/perf/Documentation/perf-diff.txt

 perf-diff(1)
-==============
+============
 
 NAME
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tools/perf/Documentation/perf-kmem.txt

 perf-kmem(1)
-==============
+============
 
 NAME
 ----

tools/perf/Documentation/perf-trace-python.txt

 perf-trace-python(1)
-==================
+====================
 
 NAME
 ----

tools/perf/Documentation/perf-trace.txt

 perf-trace(1)
-==============
+=============
 
 NAME
 ----