Fix T45617: Map UV node produces image artifacts

Basically filtering was happening twice, first time by applying weights of EWA
filter itself and then by applying subpixel offset while reading pixel values.

source/blender/compositor/intern/COM_MemoryBuffer.h

@@ -262,7 +262,7 @@ public:
 		BLI_bilinear_interpolation_fl(this->m_buffer, result, this->m_width, this->m_height, this->m_num_channels, u, v);
 	}
 
-	void readEWA(float *result, const float uv[2], const float derivatives[2][2], PixelSampler sampler);
+	void readEWA(float *result, const float uv[2], const float derivatives[2][2]);
 	
 	/**
 	 * @brief is this MemoryBuffer a temporarily buffer (based on an area, not on a chunk)