build: Remove left-over file

The file was generated when importing gnome-extensions-tool from
a standalone repository. It isn't used by the build system, and
really shouldn't have ended up in the repository at all.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/877

src/extensions-tool/meson-src.build

@@ -1,24 +0,0 @@
-sources = [
-  'commands.h',
-  'command-create.c',
-  'command-disable.c',
-  'command-enable.c',
-  'command-info.c',
-  'command-install.c',
-  'command-list.c',
-  'command-pack.c',
-  'command-prefs.c',
-  'common.h',
-  'main.c'
-]
-
-resources = gnome.compile_resources('resources',
-  'gnome-extensions-tool.gresource.xml',
-  source_dir: '.'
-)
-
-executable('gnome-extensions',
-  sources, resources,
-  dependencies: [gio_dep, gio_unix_dep, autoar_dep, json_dep],
-  install: true
-)