meta-ibm: romulus: fans: drop unused variable

meta-phosphor dropped support for native class config recipes and uses
target class config recipes by default.  Drop the reference to
PHOSPHOR_FAN_CONFIG_USE_NATIVE_SYSROOT as it is no longer used in
meta-phosphor.

(From meta-ibm rev: 0bc0301510b3371510a86fa684b72ea4d4100cf1)

Change-Id: I6b59b1429ead70c1e4ac85a1c9d66b3e04197dd5
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-ibm/meta-romulus/conf/machine/romulus.conf b/meta-ibm/meta-romulus/conf/machine/romulus.conf
index 2c3c621..32ece45 100644
--- a/meta-ibm/meta-romulus/conf/machine/romulus.conf
+++ b/meta-ibm/meta-romulus/conf/machine/romulus.conf
@@ -1,7 +1,5 @@
 KMACHINE = "aspeed"
 KERNEL_DEVICETREE = "${KMACHINE}-bmc-opp-${MACHINE}.dtb"
-
-PHOSPHOR_FAN_CONFIG_USE_NATIVE_SYSROOT = "0"
 UBOOT_MACHINE = "ast_g5_ncsi_config"
 
 PREFERRED_PROVIDER_virtual/p9-vcs-workaround = ''