python,python3: Clear more fields for src packages

This clears the CONFLICTS, PROVIDES, EXTRA_DEPENDS, and USERID fields
for -src packages.

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

lang/python/python-package.mk

@@ -40,7 +40,11 @@ define PyPackage
   define Package/$(1)-src
     $(call Package/$(1))
     DEPENDS:=
+    CONFLICTS:=
+    PROVIDES:=
+    EXTRA_DEPENDS:=
     TITLE+= (sources)
+    USERID:=
   endef
 
   define Package/$(1)-src/description

lang/python/python3-package.mk

@@ -39,7 +39,11 @@ define Py3Package
   define Package/$(1)-src
     $(call Package/$(1))
     DEPENDS:=
+    CONFLICTS:=
+    PROVIDES:=
+    EXTRA_DEPENDS:=
     TITLE+= (sources)
+    USERID:=
   endef
 
   define Package/$(1)-src/description