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OpenGL: Ditch index buffer

Seems completely unnecessary for 2D

--- a/src/Backends/Rendering/OpenGL3.cpp

+++ b/src/Backends/Rendering/OpenGL3.cpp

@@ -210,13 +210,6 @@

 	glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_id);

 	glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_buffer), NULL, GL_DYNAMIC_DRAW);

-	// Set up Index Buffer Object

-	const GLuint indices[4] = {0, 1, 2, 3};

-	GLuint index_buffer_id;

-	glGenBuffers(1, &index_buffer_id);

-	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, index_buffer_id);

-	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

-

 	// Set up the vertex attributes

 	glEnableVertexAttribArray(1);

 	glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, (GLvoid*)offsetof(VertexBuffer, vertexes));

@@ -297,7 +290,7 @@

 	vertex_buffer.vertexes[3][1] = 1.0f;

 	glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertex_buffer), &vertex_buffer);

-	glDrawElements(GL_TRIANGLE_FAN, 4, GL_UNSIGNED_INT, NULL);

+	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

 	SDL_GL_SwapWindow(window);

@@ -399,7 +392,7 @@

 	vertex_buffer.vertexes[3][1] = vertex_bottom;

 	glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertex_buffer), &vertex_buffer);

-	glDrawElements(GL_TRIANGLE_FAN, 4, GL_UNSIGNED_INT, NULL);

+	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

 }

 void Backend_Blit(Backend_Surface *source_surface, const RECT *rect, Backend_Surface *destination_surface, long x, long y, BOOL colour_key)

@@ -453,7 +446,7 @@

 	vertex_buffer.vertexes[3][1] = vertex_bottom;

 	glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertex_buffer), &vertex_buffer);

-	glDrawElements(GL_TRIANGLE_FAN, 4, GL_UNSIGNED_INT, NULL);

+	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

 }

 void Backend_ColourFill(Backend_Surface *surface, const RECT *rect, unsigned char red, unsigned char green, unsigned char blue)

@@ -602,7 +595,7 @@

 	vertex_buffer.vertexes[3][1] = vertex_bottom;

 	glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertex_buffer), &vertex_buffer);

-	glDrawElements(GL_TRIANGLE_FAN, 4, GL_UNSIGNED_INT, NULL);

+	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

 }

 void Backend_DrawGlyph(Backend_Surface *surface, Backend_Glyph *glyph, long x, long y, const unsigned char *colours)