Revert "zstd: install to staging directory"

This reverts commit 95c15aaf15f4bd5b1ebcf87d204ddf5a345197d5. It was
mistakenly pushed, and causes problems because it installs the shared
library to staging, but not to target.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/zstd/zstd.mk

@@ -6,7 +6,6 @@
 
 ZSTD_VERSION = v1.3.2
 ZSTD_SITE = $(call github,facebook,zstd,$(ZSTD_VERSION))
-ZSTD_INSTALL_STAGING = YES
 ZSTD_LICENSE = BSD-3-Clause, GPL-2.0
 ZSTD_LICENSE_FILES = LICENSE COPYING
 
@@ -47,9 +46,4 @@ define ZSTD_INSTALL_TARGET_CMDS
 		DESTDIR=$(TARGET_DIR) PREFIX=/usr -C $(@D)/programs install
 endef
 
-define ZSTD_INSTALL_STAGING_CMDS
-	$(TARGET_MAKE_ENV) $(TARGET_CONFIGURE_OPTS) $(MAKE) $(ZSTD_OPTS) \
-		DESTDIR=$(STAGING_DIR) PREFIX=/usr -C $(@D)/lib install
-endef
-
 $(eval $(generic-package))