wireguard: no longer need portability patch

Drop package/network/services/wireguard/patches/100-portability.patch

Instead pass 'PLATFORM=linux' to make since we are always building FOR
linux.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
(cherry picked from commit f06def4221)

package/network/services/wireguard/Makefile

@@ -60,6 +60,7 @@ include $(INCLUDE_DIR)/package-defaults.mk
 
 # Used by Build/Compile/Default
 MAKE_PATH:=src/tools
+MAKE_VARS += PLATFORM=linux
 
 define Build/Compile
 	$(MAKE) $(KERNEL_MAKEOPTS) M="$(PKG_BUILD_DIR)/src" modules

package/network/services/wireguard/patches/100-portability.patch

@@ -1,19 +0,0 @@
-tools: fix portability issue
-
-Check if the compiler defines __linux__, instead of assuming that the
-host OS is the same as the target OS.
-
-Signed-off-by: Felix Fietkau <nbd@nbd.name>
----
---- a/src/tools/Makefile
-+++ b/src/tools/Makefile
-@@ -36,6 +36,9 @@ endif
- endif
- 
- PLATFORM ?= $(shell uname -s | tr '[:upper:]' '[:lower:]')
-+ifeq ($(strip $(shell echo __linux__ | $(CC) -E - | grep -v '^\#')),1)
-+PLATFORM := linux
-+endif
- 
- CFLAGS ?= -O3
- CFLAGS += -std=gnu11 -D_GNU_SOURCE