build: Fix pylint checks timing out

Disable "similarity" report in pylint so as to fix the pathological
speed regression that caused most of the checks to timeout.

See pylint-dev/pylint#4120 (comment)

src/plugins/meson.build

@@ -69,7 +69,7 @@ if plugins_option != 'none'
   endif
 endif
 
-pylint_flags = ['-d', 'C0111', '-d', 'W0511', '-d', 'F0401', '-d', 'C0326' ]
+pylint_flags = ['-d', 'C0111', '-d', 'W0511', '-d', 'F0401', '-d', 'C0326', '-d', 'R0801', '-d', 'RP0801' ]
 
 # FIXME: Move custom_target to i18n.merge_file when gettext acquires plugin support.
 #        http://lists.gnu.org/archive/html/bug-gettext/2017-06/msg00001.html