graphics/mesa-devel: unbreak standalone build after 85ef7d0

$ echo DEFAULT_VERSIONS+=gl=mesa-devel >>/etc/make.conf
$ make restage check-plist
[...]
====> Checking for pkg-plist issues (check-plist)
===> Parsing plist
===> Checking for items in STAGEDIR missing from pkg-plist
===> Checking for items in pkg-plist which are not in STAGEDIR
Error: Missing: include/EGL/eglextchromium.h
===> Error: Plist issues found.
*** Error code 1

PR:		265784
Regressed by:	https://gitlab.freedesktop.org/mesa/mesa/-/commit/f5bb9dd738ac

(cherry picked from commit b9e8d13)

graphics/mesa-devel/pkg-plist

@@ -1,7 +1,6 @@
 %%VKLAYERS%%bin/mesa-overlay-control.py
 %%COINST%%@sample etc/libmap.d/mesa%%SUFFIX%%.conf.sample
 %%NO_COINST%%include/EGL/eglext_angle.h
-%%NO_COINST%%include/EGL/eglextchromium.h
 %%NO_COINST%%include/EGL/eglmesaext.h
 %%NO_COINST%%include/GL/internal/dri_interface.h
 %%NO_COINST%%include/gbm.h