Bug 7061: unnecessary global variables declared in C4::SQLHelper

Bug 7061: unnecessary global variables declared in C4::SQLHelper

Removes $tablename and $hash from global scope of C4/SQLHelper.pm.  They are never used;
all instances of $table are locally scoped to the subroutines, and $hash is never used.

This may help with persistance; if not, it's at least a bit of trivial cleanup.

To test:

1.  Search for a patron
2.  Create a Contract in Acquisitions
3.  Modify that Contract
4.  Delete that Contract

All instances should return error free.  This checks the subroutines of SQLHelper

Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>