ARM: 9072/1: mm: remove set_kernel_text_r[ow]()

After commit 5a735583 ("arm/ftrace: Use __patch_text()"), the last
and only user of these functions has gone, remove them.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>