Remove obsolete win_pdf_metafile_for_printing GN flag.

tools/gn/docs/cookbook.md

 # GYP->GN Conversion Cookbook
 
 [TOC]
 
 ## Targets
 
 | *GYP*                                            | *GN*                                               |
 |:-------------------------------------------------|:---------------------------------------------------|
 | `'type': 'static_library', 'name': 'foo',`       | `static_library("foo") {` or `source_set("foo") {` |
 | `'type': 'shared_library', 'name': 'foo',`       | `shared_library("foo") {`                          |
@@ skipping 239 matching lines @@
 | `use_gnome_keyring` (0/1)               | `is_desktop_linux` (true/false)                |                               |
 | `use_goma` (0/1)                        | `use_goma` (true/false)                        | `//build/toolchain/goma.gni`  |
 | `use_nss_certs` (0/1)                   | `use_nss_certs` (true/false)                   | `//build/config/crypto.gni` (Many of these conditions can be deleted, see the "SSL" notes on targets below.) |
 | `use_openssl` (0/1)                     | `use_openssl` (true/false)                     | `//build/config/crypto.gni` (Many of these conditions can be deleted, see the "SSL" notes on targets below.) |
 | `use_pango` (0/1)                       | `use_pango` (true/false)                       | `//build/config/ui.gni`       |
 | `use_ozone` (0/1)                       | `use_ozone` (true/false)                       | `//build/config/ui.gni`       |
 | `use_seccomp_bpf` (0/1)                 | `use_seccomp_bpf` (true/false)                 | `//build/config/features.gni` |
 | `use_udev` (0/1)                        | `use_udev` (true/false)                        | `//build/config/features.gni` |
 | `use_x11` (0/1)                         | `use_x11` (true/false)                         | `//build/config/ui.gni`       |
 | `use_xi2_mt` (0/1)                      | `use_xi2_mt` (true/false)                      | `//build/config/ui.gni`       |
-| `win_pdf_metafile_for_printing` (0/1)   | `win_pdf_metafile_for_printing` (true/false)   | `//build/config/features.gni` |
 | `win_use_allocator_shim` (0/1)          |                                                | (See "Allocator" below)       |
 
 ### Common target conversion
 
 Some targets that lots of projects depend on and how the GN ones
 correspond to GYP ones. (This is for commonly-depended-on or weird
 targets only, don't add stuff here just because you converted it.)
 
 | *GYP*                                                                              | *GN*                                     | *Notes* (see below)  |
 |:-----------------------------------------------------------------------------------|:-----------------------------------------|:---------------------|
@@ skipping 371 matching lines @@
 
 ```
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("mojo_bindings") {
   sources = [
     "foo.mojom",
   ]
 }
 ```