luacheckrc: Remove accidentally commented directive
Accidentally commented in 4b258329e6e4
This directive was removed from Prosody in d59be9befad7 followed by a
big sweep of the resulting warnings.
--- a/.luacheckrc Sat Nov 06 21:09:21 2021 +0100
+++ b/.luacheckrc Tue Jan 28 21:54:04 2020 +0100
@@ -1,6 +1,5 @@
cache = true
allow_defined_top = true
---unused_secondaries = false
max_line_length = 150
codes = true
ignore = { "411/err", "421/err", "411/ok", "421/ok", "211/_ENV" };