[expr] Remove outdated, inaccurate, irrelevant note on the actual

behavior of signed integer overflow on "most existing implementations".

Author: zygoloid

source/expressions.tex

@@ -63,9 +63,8 @@
 its type, the behavior is undefined.
 \enternote 
 \indextext{overflow}%
-most existing implementations of \Cpp ignore integer overflows.
 Treatment of division by zero, forming a remainder using a zero divisor,
-and all floating point exceptions vary among machines, and is usually
+and all floating point exceptions vary among machines, and is sometimes
 adjustable by a library function.
 \exitnote