only build manpage, and install it in correct dir

Index: doc/meson.build
--- doc/meson.build.orig
+++ doc/meson.build
@@ -1,31 +1,9 @@
-sphinx_output = custom_target(
-  'HTML documentation',
-  output: 'html',
-  input: ['index.rst', 'conf.py'],
-  command: [sphinx, '-q', '-b', 'html', '-d', '@OUTDIR@/html_doctrees', meson.current_source_dir(), '@OUTPUT@'],
-  build_by_default: true,
-  install: true,
-  install_dir: join_paths(get_option('datadir'), 'doc', meson.project_name()),
-)
-
 custom_target(
-  'upload',
-  input: sphinx_output,
-  output: 'upload',
-  build_always_stale: true,
-  command: [
-    'rsync', '-vpruz', '--delete', '@INPUT@',
-    'www.musicpd.org:/var/www/mpd/doc/mpc/',
-    '--chmod=a+rX',
-  ],
-)
-
-custom_target(
   'Manpage documentation',
-  output: 'man',
+  output: 'man1',
   input: ['index.rst', 'conf.py'],
-  command: [sphinx, '-q', '-b', 'man', '-d', '@OUTDIR@/man_doctrees', meson.current_source_dir(), '@OUTPUT@/man1'],
+  command: [sphinx, '-q', '-b', 'man', '-d', '@OUTDIR@/man_doctrees', meson.current_source_dir(), '@OUTPUT@'],
   build_by_default: true,
   install: true,
-  install_dir: get_option('datadir'),
+  install_dir: get_option('mandir'),
 )