MDEV-11836 vcol.vcol_keys_myisam fails in buildbot and outside

move TABLE::key_read into handler. Because in index merge and DS-MRR
there can be many handlers per table, and some of them use
key read while others don't. "keyread" is really per handler,
not per TABLE property.

sql/opt_range.h

@@ -1037,7 +1037,6 @@ class QUICK_RANGE_SELECT : public QUICK_SELECT_I
 {
 protected:
   /* true if we enabled key only reads */
-  bool doing_key_read;
   handler *file;
 
   /* Members to deal with case when this quick select is a ROR-merged scan */