Obsolete BUILD_BROKEN_ANDROIDMK_EXPORTS

Bug: 73959648
Test: treehugger
Change-Id: Ibecc6eb97fef6924e5d909c0393d8dfaa62c7d1d

Changes.md

@@ -194,11 +194,9 @@ you're not trying to actively debug the kernel.
 
 ## `export` and `unexport` deprecation  {#export_keyword}
 
-The `export` and `unexport` keywords have been deprecated, and will throw
-warnings or errors depending on where they are used.
+The `export` and `unexport` keywords are obsolete, and will throw errors when
+used.
 
-Early in the make system, during product configuration and BoardConfig.mk
-reading: these will throw a warnings, and will be an error in the future.
 Device specific configuration should not be able to affect common core build
 steps -- we're looking at triggering build steps to be invalidated if the set
 of environment variables they can access changes. If device specific
@@ -206,10 +204,9 @@ configuration is allowed to change those, switching devices with the same
 output directory could become significantly more expensive than it already can
 be.
 
-Later, during Android.mk files, and later tasks: these will throw errors, since
-it is increasingly likely that they are being used incorrectly, attempting to
-change the environment for a single build step, and instead setting it for
-hundreds of thousands.
+If used during Android.mk files, and later tasks, it is increasingly likely
+that they are being used incorrectly. Attempting to change the environment for
+a single build step, and instead setting it for hundreds of thousands.
 
 It is not recommended to just move the environment variable setting outside of
 the build (in vendorsetup.sh, or some other configuration script or wrapper).