scsi: docs: Remove obsolete scsi typedef text from scsi_mid_low_api

Commit 91ebc1f ("scsi: core: remove Scsi_Cmnd typedef") removed the
Scsi_cmnd typedef but it was still mentioned in a paragraph in the "SCSI
mid_level - lower_level driver interface" documentation page.  Remove this
obsolete paragraph.

Link: https://lore.kernel.org/r/20200905210211.2286172-1-nfraprado@protonmail.com
Suggested-by: Randy Dunlap <rdunlap@infradead.org>
Suggested-by: Jonathan Corbet <corbet@lwn.net>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@protonmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Documentation/scsi/scsi_mid_low_api.rst

@@ -271,12 +271,6 @@ Conventions
 First, Linus Torvalds's thoughts on C coding style can be found in the
 Documentation/process/coding-style.rst file.
 
-Next, there is a movement to "outlaw" typedefs introducing synonyms for
-struct tags. Both can be still found in the SCSI subsystem, but
-the typedefs have been moved to a single file, scsi_typedefs.h to
-make their future removal easier, for example:
-"typedef struct scsi_cmnd Scsi_Cmnd;"
-
 Also, most C99 enhancements are encouraged to the extent they are supported
 by the relevant gcc compilers. So C99 style structure and array
 initializers are encouraged where appropriate. Don't go too far,