devel: Remove hard-coded ZEPHYR_BASE environment variable

This commit removes the hard-coded `ZEPHYR_BASE` environment variable
from the Developer image to allow more flexibility for the user Zephyr
tree layout.

With this change, it is now up to the user to provide the adequate
environment configuration (e.g. setting `ZEPHYR_BASE` environment
variable, or providing west configuration file with Zephyr base path)
for Zephyr source root discovery.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Author: stephanosio

Dockerfile.devel

@@ -69,7 +69,6 @@ USER $USERNAME
 
 # Configure environment variables
 ENV DISPLAY=:0
-ENV ZEPHYR_BASE=/workdir/zephyr
 
 # Set working directory
 WORKDIR /workdir