Merge branch 'jk/arith-expansion-coding-guidelines'

The coding guideline for shell scripts instructed to refer to a
variable with dollar-sign inside arithmetic expansion to work
around a bug in old versions of dash, which is a thing of the past.
Now we are not forbidden from writing $((var+1)).

* jk/arith-expansion-coding-guidelines:
  CodingGuidelines: drop arithmetic expansion advice to use "$x"

Documentation/CodingGuidelines

@@ -95,10 +95,6 @@ For shell scripts specifically (not exhaustive):
 
  - We use Arithmetic Expansion $(( ... )).
 
- - Inside Arithmetic Expansion, spell shell variables with $ in front
-   of them, as some shells do not grok $((x)) while accepting $(($x))
-   just fine (e.g. dash older than 0.5.4).
-
  - We do not use Process Substitution <(list) or >(list).
 
  - Do not write control structures on a single line with semicolon.