Remove apache 2.2 workarounds

From trusty onwards apache 2.4 is installed. The charm no longer needs
to check for apache 2.2 configurations.

This also solves Bug #1799500 where a package like javascript-common
pre-creates the /etc/apache directory leading to a failed
register_configs.

Note: The previous fix for Bug #1799500 was incorrect.
Reverting and adding a set -e to avoid future breakage.

This will need to be backported to stable.

Change-Id: Ic6025bd10568a748e39faaf3a97b4b6a2c35a4d2
Closes-Bug: #1799500
(cherry picked from commit e9caae0a23461f3b503035e94865ccc3c8509a32)