Remove dead legacy GL Texture class

texture.hpp / texture.cpp implemented an unfinished OpenGL texture loader
(loadFromFile was a TODO stub) that had no callers — the project's texture
loading is entirely handled by VkTexture (vk_texture.hpp/cpp) after the
Vulkan migration. Remove both files and their CMakeLists entries.

include/rendering/texture.hpp

@@ -1,38 +0,0 @@
-#pragma once
-
-#include <string>
-#include <GL/glew.h>
-
-namespace wowee {
-namespace rendering {
-
-class Texture {
-public:
-    Texture() = default;
-    ~Texture();
-
-    bool loadFromFile(const std::string& path);
-    bool loadFromMemory(const unsigned char* data, int width, int height, int channels);
-
-    void bind(GLuint unit = 0) const;
-    void unbind() const;
-
-    GLuint getID() const { return textureID; }
-    int getWidth() const { return width; }
-    int getHeight() const { return height; }
-
-private:
-    GLuint textureID = 0;
-    int width = 0;
-    int height = 0;
-};
-
-/**
- * Apply anisotropic filtering to the currently bound GL_TEXTURE_2D.
- * Queries the driver maximum once and caches it. No-op if the extension
- * is not available.
- */
-void applyAnisotropicFiltering();
-
-} // namespace rendering
-} // namespace wowee