[source] rukes.mk: this patch broken grub2 builds

[LEDE Commits]

blogic pushed a commit to source.git, branch master:
https://git.lede-project.org/b957e455eb57c122d3825589a0289b22720b822b

commit b957e455eb57c122d3825589a0289b22720b822b
Author: John Crispin <john at phrozen.org>
AuthorDate: Fri Sep 1 10:17:02 2017 +0200

    rukes.mk: this patch broken grub2 builds
    
    Revert "rules.mk: add missing CPP definition"
    
    This reverts commit 569f74ef49bae9326a723050a400346686983d86.
    
    Signed-off-by: John Crispin <john at phrozen.org>
---
 rules.mk | 2 --
 1 file changed, 2 deletions(-)

diff --git a/rules.mk b/rules.mk
index 43d8efe..ed796a5 100644
--- a/rules.mk
+++ b/rules.mk
@@ -260,7 +260,6 @@ endif
 BUILD_KEY=$(TOPDIR)/key-build
 
 TARGET_CC:=$(TARGET_CROSS)gcc
-TARGET_CPP:=$(TARGET_CROSS)cpp
 TARGET_CXX:=$(TARGET_CROSS)g++
 KPATCH:=$(SCRIPT_DIR)/patch-kernel.sh
 SED:=$(STAGING_DIR_HOST)/bin/sed -i -e
@@ -301,7 +300,6 @@ TARGET_CONFIGURE_OPTS = \
   NM="$(TARGET_NM)" \
   CC="$(TARGET_CC)" \
   GCC="$(TARGET_CC)" \
-  CPP="$(TARGET_CPP)" \
   CXX="$(TARGET_CXX)" \
   RANLIB="$(TARGET_RANLIB)" \
   STRIP=$(TARGET_CROSS)strip \