Remove traces of errors due to shifts by negative amounts.

docs/control-structures.rst

@@ -521,7 +521,6 @@ An ``assert``-style exception is generated in the following situations:
 #. If you access an array or an array slice at a too large or negative index (i.e. ``x[i]`` where ``i >= x.length`` or ``i < 0``).
 #. If you access a fixed-length ``bytesN`` at a too large or negative index.
 #. If you divide or modulo by zero (e.g. ``5 / 0`` or ``23 % 0``).
-#. If you shift by a negative amount.
 #. If you convert a value too big or negative into an enum type.
 #. If you call a zero-initialized variable of internal function type.
 #. If you call ``assert`` with an argument that evaluates to false.

libsolidity/codegen/YulUtilFunctions.h

@@ -86,7 +86,6 @@ public:
 
 	/// @returns the name of a function that performs a left shift and subsequent cleanup
 	/// and, if needed, prior cleanup.
-	/// If the amount to shift by is signed, a check for negativeness is performed.
 	/// signature: (value, amountToShift) -> result
 	std::string typedShiftLeftFunction(Type const& _type, Type const& _amountType);
 	std::string typedShiftRightFunction(Type const& _type, Type const& _amountType);