tools: revise line in configure.py for clarity

* Replace unused identifier with Python convention `_`.
* Remove unneeded parentheses.
* Remove line-wrapping.

I confirmed that this doesn't change the output by running `./configure
--shared-zlib` and confirming that it created the same `common.gypi`
with and without these changes. The code changed here doesn't run unless
there is a `--shared-*` flag.

PR-URL: #36551
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>

configure.py

@@ -1248,8 +1248,7 @@ def configure_library(lib, output, pkgname=None):
   output['variables']['node_' + shared_lib] = b(getattr(options, shared_lib))
 
   if getattr(options, shared_lib):
-    (pkg_libs, pkg_cflags, pkg_libpath, pkg_modversion) = (
-        pkg_config(pkgname or lib))
+    (pkg_libs, pkg_cflags, pkg_libpath, _) = pkg_config(pkgname or lib)
 
     if options.__dict__[shared_lib + '_includes']:
       output['include_dirs'] += [options.__dict__[shared_lib + '_includes']]