[BUGFIX] Remove declare(encoding=)

AbstractWidgetViewHelper can throw warnings about invalid
declare statements if zend.multibyte is off. Those lines
were also dropped in TYPO3.Fluid, TYPO3 6.0 & TYPO3 4.7.

Change-Id: I7f4efca526249034b74ba42b1103b58831b5a2ea
Resolves: #38055
Releases: 4.5
Reviewed-on: https://review.typo3.org/25157
Reviewed-by: Wouter Wolters
Reviewed-by: Ernesto Baschny
Reviewed-by: Marc Bastian Heinrichs
Tested-by: Marc Bastian Heinrichs