ninja: Remove use of unset ninja variable 'aliasing'

Setting this variable to contain additional commands to symlink shlib
aliases was removed in commit c0bf3e8d, so it's always unset now, and
thus does nothing.

mesonbuild/backend/ninjabackend.py

@@ -1473,10 +1473,10 @@ int dummy;
                 if compiler.can_linker_accept_rsp():
                     command_template = ''' command = {executable} @$out.rsp
  rspfile = $out.rsp
- rspfile_content = $ARGS  {output_args} $in $LINK_ARGS $aliasing
+ rspfile_content = $ARGS  {output_args} $in $LINK_ARGS
 '''
                 else:
-                    command_template = ' command = {executable} $ARGS {output_args} $in $LINK_ARGS $aliasing\n'
+                    command_template = ' command = {executable} $ARGS {output_args} $in $LINK_ARGS\n'
                 command = command_template.format(
                     executable=' '.join(compiler.get_linker_exelist()),
                     output_args=' '.join(compiler.get_linker_output_args('$out'))