Replace mysql_byte with uchar and remove the #define mysql_byte from

ha_innodb.cc.  This cleanup was made possible as of r1550:

Merge changes from MySQL AB:

ChangeSet@2007-05-10 12:59:39+03:00, monty@mysql.com 
  WL#3817: Simplify string / memory area types and make things more consistent
  (first part)
  
  The following type conversions was done:
  
  - Changed byte to uchar
...