Remove needless FIXME

In this case, it seems fine to have the field be the inverse of the
flag, especially the `enable` vs `disable` terminology is clear.

src/librustdoc/config.rs

@@ -240,9 +240,6 @@ pub(crate) struct RenderOptions {
     pub(crate) resource_suffix: String,
     /// Whether to run the static CSS/JavaScript through a minifier when outputting them. `true` by
     /// default.
-    //
-    // FIXME(misdreavus): the flag name is `--disable-minification` but the meaning is inverted
-    // once read.
     pub(crate) enable_minification: bool,
     /// Whether to create an index page in the root of the output directory. If this is true but
     /// `enable_index_page` is None, generate a static listing of crates instead.