perf build: Fixup disabling of -Wdeprecated-declarations for the python scripting engine

A brown paper bag where -Wno-error=deprecated-declarations was added
from compiler output when the right thing is to add
-Wno-deprecated-declarations, fix it.

Fixes: 4ee3c4da

 ("perf scripting python: Do not build fail on deprecation warnings")
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>