usb: gadget: Remove File-backed Storage Gadget (g_file_storage).

The File-backed Storage Gadget (g_file_storage) gadget has been replaced
with Mass Storage Gadget (g_mass_storage) which uses the composite
framework.  This commit removes g_file_storage (and most references to it).

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/Documentation/DocBook/gadget.tmpl b/Documentation/DocBook/gadget.tmpl
index 6ef2f00..4017f14 100644
--- a/Documentation/DocBook/gadget.tmpl
+++ b/Documentation/DocBook/gadget.tmpl
@@ -671,7 +671,7 @@
 <para>There's a USB Mass Storage class driver, which provides
 a different solution for interoperability with systems such
 as MS-Windows and MacOS.
-That <emphasis>File-backed Storage</emphasis> driver uses a
+That <emphasis>Mass Storage</emphasis> driver uses a
 file or block device as backing store for a drive,
 like the <filename>loop</filename> driver.
 The USB host uses the BBB, CB, or CBI versions of the mass