[basic.scope.block] Reintroduce local variable

P1787R6 dropped the previous buggy uses and definition of term
_local variable_. But there're many remaining use of local variable,
and the intent seems to be block variable with automatic storage
duration. Let's try to reintroduce _local variable_ for convenience.

source/basic.tex

@@ -1297,6 +1297,7 @@
 A substatement that is also a block has only one scope.
 \end{note}
 A variable that belongs to a block scope is a \defn{block variable}.
+A block variable with automatic storage duration is a \defn{local variable}.
 \begin{example}
 \begin{codeblock}
 int i = 42;