USB: g_mass_storage: testing code from f_mass_storage.c removed

Removed code that was included when CONFIG_USB_FILE_STORAGE_TEST
was defined.  If this functionality is required one may still use
the original File-backed Storage Gadget.  It has been agreed that
testing functionality is not required in the composite function.

Also removed fsg_suspend() and fsg_resume() which were no
operations.

Moreover, storage_common.c has been modified in such a way that
defining certain macros skips parts of the file.  Those macros
are:
* FSG_NO_INTR_EP -- skips interrupt endpoint descriptors
* FSG_NO_DEVICE_STRINGS -- skips certain strings
* FSG_NO_OTG -- skips OTG descriptor

Signed-off-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>