meta-jade: Clean up phosphor-isolation distro feature

As mtjade uses the newer u-boot tree based on v2019.04, the
phosphor-isolation distro feature does not do anything.

The backdoors closed by the distro feature are now closed by default, so
no opt-in is required.

Change-Id: I779caf74f138715e0a49febbdb09d4ef78e33e0c
Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/meta-ampere/meta-jade/conf/machine/mtjade.conf b/meta-ampere/meta-jade/conf/machine/mtjade.conf
index 0266fee..bec22ca 100644
--- a/meta-ampere/meta-jade/conf/machine/mtjade.conf
+++ b/meta-ampere/meta-jade/conf/machine/mtjade.conf
@@ -6,7 +6,6 @@
 
 require conf/machine/include/ast2500.inc
 require conf/machine/include/obmc-bsp-common.inc
-require conf/distro/include/phosphor-isolation.inc
 require conf/distro/include/phosphor-aspeed-spi-master-mode.inc
 
 # Reformat SPI flash layout to 64MB