tools: drop PKG_VERSION for purely local packages

tools: drop PKG_VERSION for purely local packages

This applies to tools directory what has been done for package/ in
commit 9c170cb92f4f ("package: drop PKG_VERSION for purely local
packages"):

In the package guidelines, PKG_VERSION is supposed to be used as
"The upstream version number that we're downloading", while
PKG_RELEASE is referred to as "The version of this package Makefile".
Thus, the variables in a strict interpretation provide a clear
distinction between "their" (upstream) version in PKG_VERSION and
"our" (local OpenWrt trunk) version in PKG_RELEASE.

For local (OpenWrt-only) packages, this implies that those will only
need PKG_RELEASE defined, while PKG_VERSION does not apply following
a strict interpretation. While the majority of "our" packages actually
follow that scheme, there are also some that mix both variables or
have one of them defined but keep them at "1".

This is misleading and confusing, which can be observed by the fact
that there typically either one of the variables is never bumped or
the choice of the variable to increase depends on the person doing the
change.

Consequently, this patch aims at clarifying the situation by
consistently using only PKG_RELEASE for "our" packages. For tools/,
only three packages were affected. This fixes two of them, and
leaves the remaining wrt350nv2-builder untouched, as the code there
seems to have some versioning of its own that is treated as upstream
version in PKG_VERSION.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>