Remove hmr socket code from prod build (#76232)
Follow up to https://github.com/vercel/next.js/pull/54078, we wouldn't
want HMR related code in production bundle. Relates to
https://github.com/vercel/next.js/issues/76198 but doesn't solve that
completely.
----
<table>
<tr>
<td><img
src="https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/rKSEEwxbNzdFs9t0yyxN/5ed4dfeb-5bc6-4e14-a1e8-efef2d0e0066.png"
width="300"/></td>
<td><img
src="https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/rKSEEwxbNzdFs9t0yyxN/38e382b2-718d-4a09-b55a-6df8b4865614.png"
width="300"/></td>
</tr>
<tr>
<td colspan="2" style="text-align: center;">Size reduced from 122KB to
119KB for a trivial app router application.</td>
</tr>
</table>
