GPU: Remove int float fetch mode combination

This commit finishes removing the uses of the integer to float
vertex buffer fetch mode. Previous commits noted below already started
that process. The last usage was geometry attributes. Now integers are
converted to floats as part of the existing upload process.

The change makes the Vulkan vertex buffer type conversion unused, so
it's removed. That's nice because Vulkan vertex buffers go from 1040 to
568 bytes in size and have significantly less overhead on creation.

Related:
- 153abc372e
- 1e1ac2bb9b
- 617858e453

Pull Request: https://projects.blender.org/blender/blender/pulls/138873

source/blender/python/gpu/gpu_py_vertex_format.cc

@@ -39,7 +39,6 @@ static PyC_StringEnumItems pygpu_vertfetchmode_items[] = {
     {GPU_FETCH_FLOAT, "FLOAT"},
     {GPU_FETCH_INT, "INT"},
     {GPU_FETCH_INT_TO_FLOAT_UNIT, "INT_TO_FLOAT_UNIT"},
-    {GPU_FETCH_INT_TO_FLOAT, "INT_TO_FLOAT"},
     {0, nullptr},
 };
 
@@ -79,7 +78,7 @@ PyDoc_STRVAR(
     "      This is mainly useful for memory optimizations when you want to store values with\n"
     "      reduced precision. E.g. you can store a float in only 1 byte but it will be\n"
     "      converted to a normal 4 byte float when used.\n"
-    "      Possible values are `FLOAT`, `INT`, `INT_TO_FLOAT_UNIT` and `INT_TO_FLOAT`.\n"
+    "      Possible values are `FLOAT`, `INT`, `INT_TO_FLOAT_UNIT`.\n"
     "   :type fetch_mode: str\n");
 static PyObject *pygpu_vertformat_attr_add(BPyGPUVertFormat *self, PyObject *args, PyObject *kwds)
 {