Remove spinlocks and atomics from meson_options.txt.

Commits e2562667 and 81385261 removed the configure equivalents, but
forgot to remove these options from meson_options.txt.

Revealed by the fact that build farm animals rorqual and francolin
didn't fail, despite being configured to set those options to off.  They
should now fail with unknown option, until they are adjusted.

meson_options.txt

@@ -49,12 +49,6 @@ option('injection_points', type: 'boolean', value: false,
 option('PG_TEST_EXTRA', type: 'string', value: '',
   description: 'Enable selected extra tests')
 
-option('atomics', type: 'boolean', value: true,
-  description: 'Use atomic operations')
-
-option('spinlocks', type: 'boolean', value: true,
-  description: 'Use spinlocks')
-
 option('PG_GIT_REVISION', type: 'string', value: 'HEAD',
   description: 'git revision to be packaged by pgdist target')