Revert "[gn check] Enable //chrome/test:browser_tests"

This reverts commit 3f863436.

Reason for revert: suspect of breaking the build
https://ci.chromium.org/p/chrome/builders/ci/chromeos-eve-chrome/14902

Original change's description:
> [gn check] Enable //chrome/test:browser_tests
>
> This involves the following:
>
> - Eliminating many unneeded includes that cause unnecessary "gn check"
>   problems
> - Adding "nogncheck" to some conditionally-included headers in
>   //content. This was a pre-existing issue (the relevant targets are
>   conditionally depended on in GN, which doesn't take into account
>   conditionality when analyzing includes); it's unclear why GN check
>   started complaining about it with the changes in this CL, but the fix
>   is correct in any case given the problem.
> - Allow //chrome/test:browser_tests to depend on //pdf:pdf_internal.
>   This is due to a real dependence of
>   //chrome/browser/chrome_find_request_manager_browsertest.cc on
>   //pdf/document_loader_impl.h for a constant defined in that header
>   file.
>
> Bug: 1158929
> Change-Id: I87a082a1312306b918cfb730695cd3fada617ae3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2905653


> Commit-Queue: Colin Blundell <blundell@chromium.org>
> Reviewed-by: Jochen Eisinger <jochen@chromium.org>
> Reviewed-by: James Cook <jamescook@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#886224}

Bug: 1158929
Change-Id: I6f9d3f80f957ebe3cf00b62c5a174259958cdaa8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2909586
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Mikel Astiz <mastiz@google.com>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#886234}