bitbake: lib/bb/build: remove mention of OE_EXTRA_IMPORTS

This is an OpenEmbedded-specific variable that is no longer used[1].

[1] oe-core 1f56155e ("base: Switch to use addpylib directive and
    BB_GLOBAL_PYMODULES")

(Bitbake rev: 34bfa55a3c14f5d1d6bb3e31b747906fa7cb99c3)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/build.py

@@ -397,7 +397,7 @@ def create_progress_handler(func, progress, logfile, d):
         # Use specified regex
         return bb.progress.OutOfProgressHandler(d, regex=progress.split(':', 1)[1], outfile=logfile)
     elif progress.startswith("custom:"):
-        # Use a custom progress handler that was injected via OE_EXTRA_IMPORTS or __builtins__
+        # Use a custom progress handler that was injected via other means
         import functools
         from types import ModuleType