remove MOCKGPU workaround in rand (tinygrad#9565)

also `requires_grad_` to save a line

Author: chenyuxyz

tinygrad/tensor.py

@@ -507,9 +507,6 @@ def rand(*shape, device:str|None=None, dtype:DTypeLike|None=None, contiguous:boo
     if (numel := prod(shape)) == 0: return Tensor.zeros(shape, device=_device, dtype=dtype, **kwargs)
     num = ceildiv(numel * dtype.itemsize, 4)
 
-    # when using MOCKGPU and NV generate rand on CPU
-    if getenv("MOCKGPU") and device.startswith("NV"): device = "CPU"
-
     # generate per device seeds and rng counter if we haven't seen this device yet
     if device not in Tensor._device_seeds:
       Tensor._device_seeds[device] = Tensor(
@@ -532,12 +529,7 @@ def rand(*shape, device:str|None=None, dtype:DTypeLike|None=None, contiguous:boo
     one = Tensor.ones_like(bits, device=bits.device, dtype=dtype).bitcast(uint_dtype)
     bits = bits.rshift((dtype.itemsize * 8) - nmant).bitwise_or(one)
     # bitcast back to the original dtype and reshape
-    out = bits.bitcast(dtype)[:numel].sub(1).reshape(shape)
-
-    # move back to the original device if we were using MOCKGPU
-    if getenv("MOCKGPU") and _device: out = out.to(_device)
-
-    out.requires_grad = kwargs.get("requires_grad")
+    out = bits.bitcast(dtype)[:numel].sub(1).reshape(shape).requires_grad_(kwargs.get("requires_grad"))
     return out.contiguous() if contiguous else out
 
   # ***** creation helper functions *****