vala: Don't assist with path for libintl

It masks an issue with glib's pkg-config file which is parsed at
runtime by valac. glib-2.0.pc should have the relevant parts for -lintl.

Library/Formula/vala.rb

@@ -33,7 +33,7 @@ def install
     valac_args = [ # Build with debugging symbols.
       "-g",
       # Use Homebrew's default C compiler.
-      "--cc=#{ENV.cc} -L#{Formula["gettext"].opt_lib}",
+      "--cc=#{ENV.cc}",
       # Save generated C source code.
       "--save-temps",
       # Vala source code path.