Remove usages of JQuery aliases that have been removed

Anything that uses element.load() or unload() or error() will now be broken (see issue tracker).

git grep "\.\(load\|unload\|error\)("

• theme/bootstrapbase/amd/src/bootstrap.js

is one confirmed usage. MDL-55325 fixed a usage in LTI code. We should search again and make sure no other usages are present before completing this issue.