Drop 'fmt' target and duplicated clang-format script

build-aux/source-format handles both c++ and python, and we can't
seem to do this through meson anymore because... i don't know why.

Author: falconindy

Diff for: build-aux/clang-format

@@ -128,12 +128,6 @@ install_data(
   rename : ['_auracle'],
   install_dir : join_paths(get_option('datadir'), 'zsh/site-functions'))
 
-run_target(
-  'fmt',
-  command : [
-    join_paths(meson.project_source_root(), 'build-aux/source-format')
-  ])
-
 run_target(
   'tidy',
   command : [