pyln: Default to DEVELOPER=0 when running outside of tree

`DEVELOPER=1` assumes that the binary has been compiled with developer set to
true, which might not be the case for plugin developers. Setting this to 0 by
default has no effect in c-lightning since we always at least set it in
`config.vars` but may prevent some issues outside.

contrib/pyln-testing/pyln/testing/utils.py

@@ -63,7 +63,7 @@ def env(name, default=None):
 
 VALGRIND = env("VALGRIND") == "1"
 TEST_NETWORK = env("TEST_NETWORK", 'regtest')
-DEVELOPER = env("DEVELOPER", "1") == "1"
+DEVELOPER = env("DEVELOPER", "0") == "1"
 TEST_DEBUG = env("TEST_DEBUG", "0") == "1"
 SLOW_MACHINE = env("SLOW_MACHINE", "0") == "1"
 TIMEOUT = int(env("TIMEOUT", 180 if SLOW_MACHINE else 60))