Remove some duplicated preferences for CHEBFUN2 which should be extracted from the tech level anyway.

Also removing the 'scale' pref, which should now be passed as data.

Most of the changes in this commit as simply changing the tolerances for CHEBFUN2 tests, which were using pref.cheb2.eps.
Merge pull request #877 from chebfun/fix-chebfun2-prefs

Remove some duplicated preferences for CHEBFUN2