package/pkg-python.mk: do not set empty variables

Similarly to what we just did for conditionally-set-empty variables,
unconditionally setting empty variables serves no purpose in Makefiles,
as unset variables are just expanded as empty...

Even though we have numerous python packages, the speed gain was not
measurable, with delta much less than the noise.

Still, for consistency, we just do not set those variables.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/pkg-python.mk

@@ -127,7 +127,6 @@ $(2)_BASE_INSTALL_STAGING_OPTS = $$(PKG_PYTHON_DISTUTILS_INSTALL_STAGING_OPTS)
 else
 $(2)_BASE_ENV         = $$(HOST_PKG_PYTHON_DISTUTILS_ENV)
 $(2)_BASE_BUILD_TGT   = build
-$(2)_BASE_BUILD_OPTS   =
 $(2)_BASE_INSTALL_OPTS = $$(HOST_PKG_PYTHON_DISTUTILS_INSTALL_OPTS)
 endif
 # Setuptools
@@ -135,13 +134,11 @@ else ifeq ($$($(2)_SETUP_TYPE),setuptools)
 ifeq ($(4),target)
 $(2)_BASE_ENV         = $$(PKG_PYTHON_SETUPTOOLS_ENV)
 $(2)_BASE_BUILD_TGT   = build
-$(2)_BASE_BUILD_OPTS   =
 $(2)_BASE_INSTALL_TARGET_OPTS  = $$(PKG_PYTHON_SETUPTOOLS_INSTALL_TARGET_OPTS)
 $(2)_BASE_INSTALL_STAGING_OPTS = $$(PKG_PYTHON_SETUPTOOLS_INSTALL_STAGING_OPTS)
 else
 $(2)_BASE_ENV         = $$(HOST_PKG_PYTHON_SETUPTOOLS_ENV)
 $(2)_BASE_BUILD_TGT   = build
-$(2)_BASE_BUILD_OPTS   =
 $(2)_BASE_INSTALL_OPTS = $$(HOST_PKG_PYTHON_SETUPTOOLS_INSTALL_OPTS)
 endif
 else