libopenmpt: fix leftover from version bump

- the patch should no be needed anymore because it was fixed in libopenmpt 0.2-beta17

packages/addons/depends/audio/libopenmpt/patches/libopenmpt-bug-769.patch

@@ -1,14 +0,0 @@
-Index: soundlib/tuning.cpp
-===================================================================
---- a/soundlib/tuning.cpp	(revision 6294)
-+++ b/soundlib/tuning.cpp	(working copy)
-@@ -375,7 +375,8 @@
- 	if(!IsOfType(TT_GROUPGEOMETRIC)) return 0;
- 
- 	if(note >= 0) return note % GetGroupSize();
--	else return (GetGroupSize() -  (abs(note) % GetGroupSize())) % GetGroupSize();
-+	// static_cast<int>(note) because g++-6 template-disables std::abs overloads for 8bit and 16bit integer types via std::enable_if.
-+	else return (GetGroupSize() - (std::abs(static_cast<int>(note)) % GetGroupSize())) % GetGroupSize();
- }
- 
-