MAINTAINERS: remove iMX5 section

commit 784a90c0 ("ARM i.MX: Merge i.MX5 support into mach-imx")
merged the files, remove the iMX5 section.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Amit Kucheria <amit.kucheria@canonical.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>