Remove redundant uses of cmake -E env

- In GncAddTest, set_tests_properties() is already setting the env
- In the other uses, there is no change to the environment

po/CMakeLists.txt

@@ -19,8 +19,7 @@ foreach (lingua ${ALL_LINGUAS})
 
   add_custom_command(
       OUTPUT ${_MO_FILE}
-      COMMAND ${CMAKE_COMMAND} -E env
-        ${GETTEXT_MSGFMT_EXECUTABLE}
+      COMMAND ${GETTEXT_MSGFMT_EXECUTABLE}
             -o ${_MO_FILE} ${CMAKE_CURRENT_SOURCE_DIR}/${lingua}.po
       DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/${lingua}.po
   )