Remove obsolete comments in pkg-config-wrapper

The related code was removed in
https://codereview.chromium.org/1580643002.

BUG=none

Review-Url: https://codereview.chromium.org/1934243002
Cr-Original-Commit-Position: refs/heads/master@{#391022}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a814b7541ca7222d7c1362385ad0e0f293a437a3

linux/pkg-config-wrapper

@@ -11,9 +11,6 @@
 # This assumption is valid for a range of sysroots, in particular: a
 # LSB-compliant root filesystem mounted at the sysroot, and a board build
 # directory of a Chromium OS chroot.
-# Additional directories containing .pc files may be specified by setting
-# the PKG_CONFIG_PATH environment variable- these will be prepended to the
-# generated paths.
 
 set -o nounset
 set -o errexit