meson: Drop stale comment about making valgrind conditional.

It was fixed in 5c2ff5773a707519f6a773126f201c4e1e8a42d7.

Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Tested-by: Timothy Arceri <tarceri@itsqueeze.com>
diff --git a/meson.build b/meson.build
index d8a8bb0..ce97fa9 100644
--- a/meson.build
+++ b/meson.build
@@ -695,7 +695,6 @@
   pre_args += '-DUSE_LIBGLVND=1'
 endif
 
-# TODO: make this conditional
 if with_valgrind != 'false'
   dep_valgrind = dependency('valgrind', required : with_valgrind == 'true')
   if dep_valgrind.found()