[docs] Update docs on closure to match current behavior. (#23142)

Closure is not automatically run in -O3 by default.

Author: brendandahl

docs/emcc.txt

@@ -252,7 +252,7 @@ Options that are modified or new in *emcc* are listed below:
 "--closure 0|1|2"
    [link] Runs the *Closure Compiler*. Possible values are:
 
-      * "0": No closure compiler (default in "-O2" and below).
+      * "0": No closure compiler (default).
 
       * "1": Run closure compiler. This greatly reduces the size of
         the support JavaScript code (everything but the WebAssembly or
@@ -277,9 +277,6 @@ Options that are modified or new in *emcc* are listed below:
        before the closure-compiled code runs, because then it will
        reuse that variable.
 
-     * Closure is only run if JavaScript opts are being done ("-O2" or
-       above).
-
 "--closure-args=<args>"
    [link] Pass arguments to the *Closure compiler*. This is an
    alternative to "EMCC_CLOSURE_ARGS".

site/source/docs/tools_reference/emcc.rst

@@ -262,15 +262,14 @@ Options that are modified or new in *emcc* are listed below:
   [link]
   Runs the :term:`Closure Compiler`. Possible values are:
 
-    - ``0``: No closure compiler (default in ``-O2`` and below).
+    - ``0``: No closure compiler (default).
     - ``1``: Run closure compiler. This greatly reduces the size of the support JavaScript code (everything but the WebAssembly or asm.js). Note that this increases compile time significantly.
     - ``2``: Run closure compiler on *all* the emitted code, even on **asm.js** output in **asm.js** mode. This can further reduce code size, but does prevent a significant amount of **asm.js** optimizations, so it is not recommended unless you want to reduce code size at all costs.
 
   .. note::
 
     - Consider using ``-sMODULARIZE`` when using closure, as it minifies globals to names that might conflict with others in the global scope. ``MODULARIZE`` puts all the output into a function (see ``src/settings.js``).
     - Closure will minify the name of `Module` itself, by default! Using ``MODULARIZE`` will solve that as well. Another solution is to make sure a global variable called `Module` already exists before the closure-compiled code runs, because then it will reuse that variable.
-    - Closure is only run if JavaScript opts are being done (``-O2`` or above).
 
 ``--closure-args=<args>``
    [link]