Revert "Enable unsafe libc calls in Chromium's unsafe buffer paths file."

This reverts commit b5e047c7765e69ff5cd40525dc11b627f6a9f83b.

Reason for revert:
LUCI Bisection has identified this change as the culprit of a build failure. See the analysis: https://ci.chromium.org/ui/p/chromium/bisection/compile-analysis/b/8719120644971767441

Sample failed build: https://ci.chromium.org/b/8719120644971767441

If this is a false positive, please report it at http://b.corp.google.com/createIssue?component=1199205&description=Analysis%3A+https%3A%2F%2Fchromium-review.googlesource.com%2Fc%2Fchromium%2Fsrc%2F%2B%2F6393815&format=PLAIN&priority=P3&title=Wrongly+blamed+https%3A%2F%2Fci.chromium.org%2Fui%2Fp%2Fchromium%2Fbisection%2Fcompile-analysis%2Fb%2F8719120644971767441&type=BUG

Original change's description:
> Enable unsafe libc calls in Chromium's unsafe buffer paths file.
>
> One-line change to ease revert if some untestable downstream build
> breaks with an `error: ... is unsafe` warning.
>
> Bug: 390223051
> Change-Id: I5852938e12745d8f859d207d55f679f8e56ab137
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6393815
> Reviewed-by: Daniel Cheng <dcheng@chromium.org>
> Mega-CQ: Tom Sepez <tsepez@chromium.org>
> Commit-Queue: Tom Sepez <tsepez@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1439688}
>

Bug: 390223051
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I289079a905c2436b9db8385e10e14a8ed5e5d564
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6410571
Commit-Queue: luci-bisection@appspot.gserviceaccount.com <luci-bisection@appspot.gserviceaccount.com>
Bot-Commit: luci-bisection@appspot.gserviceaccount.com <luci-bisection@appspot.gserviceaccount.com>
Owners-Override: luci-bisection@appspot.gserviceaccount.com <luci-bisection@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1439705}

build/config/unsafe_buffers_paths.txt

@@ -5,7 +5,7 @@
 # See `docs/unsafe_buffers.md`.
 
 # Checks to enable
-.buffers,libc
+.buffers
 
 # Directories to exempt from checks
 -base/allocator/