west: run_common.py: Remove redundant 'if'

Fixes this pylint warning:

    scripts/west_commands/run_common.py:175:12: R1719: The if expression
    can be replaced with 'test' (simplifiable-if-expression)

Fixing pylint warnings for a CI check.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>
diff --git a/scripts/west_commands/run_common.py b/scripts/west_commands/run_common.py
index ea86e39..90a69c4 100644
--- a/scripts/west_commands/run_common.py
+++ b/scripts/west_commands/run_common.py
@@ -172,7 +172,7 @@
         return args.build_dir
 
     guess = config.get('build', 'guess-dir', fallback='never')
-    guess = True if guess == 'runners' else False
+    guess = guess == 'runners'
     dir = find_build_dir(None, guess)
 
     if dir and is_zephyr_build(dir):