build.config: drop setting of BUILDTOOLS_PREBUILT_BIN

to use the default value specified in build.config.common.
Otherwise the tools in build-tools used will not be found,
like the build error reported here[1]:
    build/ line 983: soong_zip: command not found


Test: build the x15 4.14 kernel successfully

Change-Id: I3a40d42ecb37dcbff527291eff7796162f62f3e9
Signed-off-by: Yongqin Liu <>
1 file changed