Revert "MDL-41106 cache: several fixes for the session cache."

This reverts commit 89182546a0ae93a2aef79383bac902c77c7801f8.
This reverts commit 170b05362a82b2c1f5353551b7bd6fe4246fe951.
This reverts commit 2e9d5a534e8e3045923055baa1609d66cec0affe.
Merge branch 'MDL-40896' of git://github.com/timhunt/moodle

Conflicts:
	theme/bootstrapbase/style/moodle.css
Merge branch 'master_MDL-39572' of https://github.com/totara/moodle
MDL-36002 keyboard drag drop: Hidden activities and labels

Get the correct title for hidden activities and labels.
Merge branch 'MDL-30839-master' of git://github.com/phalacee/moodle
MDL-41291 cache: Use fread to avoid race conditions
MDL-41222 Remove unnecessary course cache rebuild
Automatically generated installer lang files
MDL-41304: Hide and handle LDAP error when user not in context being checked
Merge branch 'MDL-39980' of git://github.com/timhunt/moodle
Merge branch 'MDL-39236-master' of git://github.com/nadavkav/moodle
Merge branch 'WIP-MDL-36044-master' of git://github.com/nadavkav/moodle
MDL-41231 - mod_data: Export to portfolio and delete selected now work together.
Merge branch 'MDL-38203' of git://github.com/timhunt/moodle
Merge branch 'w33_MDL-39474_m26_debugdeveloper' of https://github.com/skodak/moodle

Conflicts:
	lib/upgrade.txt
Merge branch 'MDL-36002-master' of git://github.com/damyon/moodle

Conflicts:
	theme/bootstrapbase/style/moodle.css
Merge branch 'MDL-39956-master' of git://github.com/FMCorz/moodle
Merge branch 'MDL-41122_master' of git://github.com/kastashov/moodle
Merge branch 'MDL-39957_master' of https://github.com/markn86/moodle
Merge branch 'MDL-41036' of git://github.com/timhunt/moodle