python: use default host build prefix, remove cross-compile workarounds for host

The sets host Python's prefix and exec-prefix to the same value
($(STAGING_DIR)/host for packages, as currently defined in
include/host-build.mk), which avoids the case where pyconfig.h is
not in the same location as Python's other header files (see
https://bugs.python.org/issue896330).

This also removes some cross compilation workarounds
(_python_sysroot/prefix/exec_prefix, disabling byte-compilation,
__PYVENV_LAUNCHER__) that are not necessary when compiling packages
for host.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

lang/python/Makefile

@@ -1,5 +1,5 @@
 #
-# Copyright (C) 2006-2015 OpenWrt.org
+# Copyright (C) 2006-2016 OpenWrt.org
 #
 # This is free software, licensed under the GNU General Public License v2.
 # See /LICENSE for more information.
@@ -12,7 +12,7 @@ include ./files/python-package.mk
 
 PKG_NAME:=python
 PKG_VERSION:=$(PYTHON_VERSION).$(PYTHON_VERSION_MICRO)
-PKG_RELEASE:=4
+PKG_RELEASE:=5
 
 PKG_SOURCE:=Python-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=https://www.python.org/ftp/python/$(PKG_VERSION)
@@ -144,7 +144,7 @@ define Build/InstallDev
 		$(PKG_INSTALL_DIR)/usr/include/python$(PYTHON_VERSION) \
 		$(1)/usr/include/
 	$(CP) \
-		$(STAGING_DIR)/host/usr/lib/python$(PYTHON_VERSION) \
+		$(STAGING_DIR)/host/lib/python$(PYTHON_VERSION) \
 		$(PKG_INSTALL_DIR)/usr/lib/libpython$(PYTHON_VERSION).so* \
 		$(1)/usr/lib/
 	$(CP) \
@@ -221,7 +221,6 @@ HOST_CONFIGURE_ARGS+= \
 	--without-cxx-main \
 	--without-pymalloc \
 	--with-threads \
-	--prefix=$(STAGING_DIR)/host/usr \
 	--with-system-expat=$(STAGING_DIR)/host \
 	--with-ensurepip=upgrade \
 	CONFIG_SITE= \