Remove pointless condition in ModuleHandler::install()

Problem/Motivation

ModuleHandler::install() contains the following code:

if ($enable_dependencies) {
  ...
  // Do something (but this does not mess with $enable_dependencies itself).
  ...
  if ($enable_dependencies) {
    ...
  }
  ...
}

The inner if-condition is pointless as it will never be FALSE.

Proposed resolution

Remove the pointless condition and inline the contained code.

Remaining tasks

User interface changes

API changes