meson: Don't fail install script if file doesn't exist

Depending on which optional features are enabled, the NSS module
might not have been built, which means the custom install script
will fail to remove the file. Let's pass -f so it succeeds regardless
of whether the file exists or not.

meson.build

@@ -2624,7 +2624,7 @@ foreach dict : modules
         if is_nss
                 # We cannot use shared_module because it does not support version suffix.
                 # Unfortunately shared_library insists on creating the symlink…
-                meson.add_install_script(sh, '-c', 'rm $DESTDIR@0@/lib@1@.so'.format(libdir, name),
+                meson.add_install_script(sh, '-c', 'rm -f $DESTDIR@0@/lib@1@.so'.format(libdir, name),
                                          install_tag : 'nss')
                 nss_targets += lib
         endif