bcoin: clean up install

Closes #63496.

Signed-off-by: FX Coudert <fxcoudert@gmail.com>
Signed-off-by: BrewTestBot <1589480+BrewTestBot@users.noreply.github.com>

Formula/bcoin.rb

@@ -19,8 +19,6 @@ class Bcoin < Formula
   depends_on "node"
 
   def install
-    # These dirs must exists before npm install.
-    mkdir_p libexec/"lib"
     system "#{Formula["node"].libexec}/bin/npm", "install", *Language::Node.std_npm_install_args(libexec)
     (bin/"bcoin").write_env_script libexec/"bin/bcoin", PATH: "#{Formula["node"].opt_bin}:$PATH"
   end