Themes: Fix doubletime_multiline scm_prompt

[mikejamestx]

Fix errors in doubletime_multiline and doubletime_multiline_pyonly themes caused by missing doubletime_scm_prompt function.

Description

Replace calls to doubletime_scm_prompt with scm_prompt within prompt_setter

Motivation and Context

The doubletime_scm_prompt function was removed in favor of scm_prompt in commit dff892e. This caused the doubletime_multiline and doubletime_multiline_pyonly themes to raise errors when generating prompts.

How Has This Been Tested?

Manually tested on Ubuntu 20.04 (WSL) and on CentOS 7

Screenshots (if appropriate):

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• If my change requires a change to the documentation, I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• If I have added a new file, I also added it to clean_files.txt and formatted it using lint_clean_files.sh.
• I have added tests to cover my changes, and all the new and existing tests pass.

[davidpfarrell]

Wonder how these got missed at the time of the conversion?

Changes seem to match original changes made to doubletime.theme.bash, sooo

Approved and thanks !