build/pkgs/rpy2: switch to the standard python package spkg-configure.m4

Our system package lists are generated with a special case that looks
for SAGE_PYTHON_PACKAGE_CHECK, so switching this spkg-configure.m4 to
use it should prevent rpy2 from being included in the standard package
list.

Author: orlitzky

build/pkgs/rpy2/spkg-configure.m4

@@ -1,14 +1 @@
-SAGE_SPKG_CONFIGURE([rpy2], [
-    sage_spkg_install_rpy2=yes
-  ], [dnl REQUIRED-CHECK
-    AC_REQUIRE([SAGE_SPKG_CONFIGURE_R])
-    dnl rpy2 is only needed when there is a usable system R
-    AS_VAR_IF([sage_spkg_install_r], [yes], [dnl
-        AS_VAR_IF([sage_use_system_r], [installed], [dnl
-            dnl Legacy SPKG installation of r
-            AS_VAR_SET([SPKG_REQUIRE], [yes])
-        ], [dnl No system package, no legacy SPKG installation
-            AS_VAR_SET([SPKG_REQUIRE], [no])
-        ])
-    ])
-])
+SAGE_SPKG_CONFIGURE([rpy2], [SAGE_PYTHON_PACKAGE_CHECK([rpy2])])