nmap: remove redundant --static flag to pkg-config

The pkg-config tool is automatically passing --static when BR2_STATIC_LIBS
is set (see package/pkgconf/pkgconf.mk), so no need to pass it explicitly
from package .mk files.

Additionally, replace a missed occurrence of $(shell) with backticks.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/nmap/nmap.mk

@@ -30,7 +30,7 @@ NMAP_POST_PATCH_HOOKS += NMAP_WRAPPER_EXEC
 ifeq ($(BR2_PACKAGE_OPENSSL),y)
 NMAP_CONF_OPTS += --with-openssl="$(STAGING_DIR)/usr"
 NMAP_DEPENDENCIES += host-pkgconf openssl
-NMAP_LIBS_FOR_STATIC_LINK += $(shell $(PKG_CONFIG_HOST_BINARY) --libs --static openssl)
+NMAP_LIBS_FOR_STATIC_LINK += `$(PKG_CONFIG_HOST_BINARY) --libs openssl`
 else
 NMAP_CONF_OPTS += --without-openssl
 endif