docs: do not require aiohttp to build

It pulls in 22 (!!!) dependencies and is only needed in CI for a trivial
lint of the HTML docs. This is a big problem for people that simply want
to compile the manpage. Let the tests fail at test time if this
dependency isn't available.

Fixes: 74aab8a42c

docs/meson.build

@@ -1,7 +1,7 @@
 project('Meson documentation', version: '1.0')
 
 yaml_modname = get_option('unsafe_yaml') ? 'yaml' : 'strictyaml'
-py = import('python').find_installation('python3', modules: [yaml_modname, 'aiohttp'], required: false)
+py = import('python').find_installation('python3', modules: [yaml_modname], required: false)
 if not py.found()
     error(f'Cannot build documentation without yaml support')
 endif