[audio_to_spectrogram] Fix when to use catkin_install_python

[pazeshun]

I found another issue of #2743 other than #2851.

Conditional branch for catkin_install_python is wrong only in audio_to_spectrogram.

Correct (jsk_recognition_msgs):

jsk_recognition/jsk_recognition_msgs/CMakeLists.txt

Lines 145 to 163 in c80a511

	if($ENV{ROS_DISTRO} STREQUAL "indigo") # on noetic it needs catkin_install_python to support Python3 and it does not work on indigo for some reason...
	install(DIRECTORY scripts
	DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}
	USE_SOURCE_PERMISSIONS
	)
	else()
	install(DIRECTORY scripts
	DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}
	USE_SOURCE_PERMISSIONS
	PATTERN "*"
	PATTERN "*/*.py" EXCLUDE
	)
	file(GLOB SCRIPT_PROGRAMS scripts/*.py)
	catkin_install_python(
	PROGRAMS ${SCRIPT_PROGRAMS}
	DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}/scripts
	)
	endif()

On indigo, catkin_install_python is not used.

Wrong (audio_to_spectrogram):

jsk_recognition/audio_to_spectrogram/CMakeLists.txt

Lines 20 to 38 in c80a511

	if(NOT $ENV{ROS_DISTRO} STREQUAL "indigo") # on noetic it needs catkin_install_python to support Python3 and it does not work on indigo for some reason...
	install(DIRECTORY scripts
	DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}
	USE_SOURCE_PERMISSIONS
	)
	else()
	install(DIRECTORY scripts
	DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}
	USE_SOURCE_PERMISSIONS
	PATTERN "*"
	PATTERN "*/*.py" EXCLUDE
	)
	file(GLOB SCRIPT_PROGRAMS scripts/*.py)
	catkin_install_python(
	PROGRAMS ${SCRIPT_PROGRAMS}
	DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}/scripts
	)
	endif()

Not on indigo, catkin_install_python is not used.