ANDROID: build.config.allmodconfig: Enable hermetic builds

This was previously not possible due to the lack of kernel module
signing support in BoringSSL.

Said support has now landed in Kernel Build Tools.

Fixes: bce40b72a3 ("ANDROID: Disable hermetic toolchain for allmodconfig builds")
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Change-Id: Ideddac33d8d79f2819a9f68e3e80a0b045e58907

build.config.allmodconfig

@@ -1,7 +1,5 @@
 DEFCONFIG=allmodconfig
 
-HERMETIC_TOOLCHAIN=0
-
 POST_DEFCONFIG_CMDS="update_config"
 function update_config() {
     ${KERNEL_DIR}/scripts/config --file ${OUT_DIR}/.config \