perf completion: Strip function_exists ()

Use "type" to check existence consistently.
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/1372941691-14684-6-git-send-email-artagnon@gmail.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/bash_completion

 # perf completion
 
-function_exists()
-{
-	declare -F $1 > /dev/null
-	return $?
-}
-
-function_exists __ltrim_colon_completions ||
+type __ltrim_colon_completions &>/dev/null ||
 __ltrim_colon_completions()
 {
 	if [[ "$1" == *:* && "$COMP_WORDBREAKS" == *:* ]]; then