bitbake: replace comment added in conf files

The patch that implements removeConfigurationVar method was made before
merging the patch that replaces "added by bitbake" with "added by hob".
This patch corrects this issue.

[YOCTO #5284]
Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>