Shave off about a minute from builds

BR2_REPRODUCIBLE performs several things related to timestamps,
hostnames, etc. One extra thing which it does is disabling
multithreading in `xz` compression of the rootfs tarball. On my laptop
with a i5-6300U CPU and an almost no-op rebuild (`time make
cla-sysrepo-reconfigure rootfs-czechlight-rauc`), this item has just
shortened the build time from 3m10s to 2m13s.

A CI build prior to this patch takes a little less than 20min. If the
speedup is at least as good, it means that the build will become at
least 5% faster, and that's IMHO a pretty nice feature.

Change-Id: I8bb22f388c17bbb9ef56e989cd7255ec4cee1359
diff --git a/configs/czechlight_beaglebone_defconfig b/configs/czechlight_beaglebone_defconfig
index dcb0b17..563e628 100644
--- a/configs/czechlight_beaglebone_defconfig
+++ b/configs/czechlight_beaglebone_defconfig
@@ -5,7 +5,6 @@
 BR2_STRIP_EXCLUDE_FILES="cla-* netopeer2* sysrepo* libsysrepo* libSysrepo* libnetconf2* libyang* sysrepo-cli"
 BR2_STRIP_EXCLUDE_DIRS="/usr/lib/libyang /usr/lib/sysrepo"
 BR2_GLOBAL_PATCH_DIR="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/common/patches"
-BR2_REPRODUCIBLE=y
 BR2_PER_PACKAGE_DIRECTORIES=y
 BR2_SSP_STRONG=y
 BR2_TOOLCHAIN_EXTERNAL=y
diff --git a/configs/czechlight_clearfog_defconfig b/configs/czechlight_clearfog_defconfig
index cd2f506..7a0ee53 100644
--- a/configs/czechlight_clearfog_defconfig
+++ b/configs/czechlight_clearfog_defconfig
@@ -7,7 +7,6 @@
 BR2_STRIP_EXCLUDE_FILES="cla-* netopeer2* sysrepo* libsysrepo* libSysrepo* libnetconf2* libyang* sysrepo-cli"
 BR2_STRIP_EXCLUDE_DIRS="/usr/lib/libyang /usr/lib/sysrepo"
 BR2_GLOBAL_PATCH_DIR="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/common/patches"
-BR2_REPRODUCIBLE=y
 BR2_PER_PACKAGE_DIRECTORIES=y
 BR2_SSP_STRONG=y
 BR2_TOOLCHAIN_EXTERNAL=y