[colorcorrection] Make GammaRamp non-copyable

Summary:
GammaRamp deletes an array in the destructor thus we have to either
declare our own copy constructor and copy assignment operator or
delete them both.

GammaRamp looks more like an identity rather than a value so both copy
constructor and copy assignment operator were deleted.

Test Plan: Compiles.

Reviewers: KWin, romangg

Reviewed By: KWin, romangg

Subscribers: kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D16023