Assert Reason can have storage pop inside

[ritzdorf]

Version Information

• vyper Version (output of vyper --version OR linkable commit hash vyperlang/vyper@commitish): 0.4.0rc5+commit.98370f50

Issue description

The assert reason is supposed to be a "constant" function. Function calls and external calls are blocked. However, pops are allowed.

POC

This compiles successfully:

x: DynArray[uint256, 2] 

@deploy
def __init__():
    self.x = [1, 1]

@external
def bar():
    b: bool = False
    assert b, uint2str(self.x.pop())