lib/helpers: Don't rm "$profile_path" before writing to it

[punchagan]

Description, Motivation and Context

When the file is being re-created, we write to it, instead of appending to
it. So, the rm here is unnecessary and prevents users from linking the profile
file to another location that is potentially under version control. For
instance, once could link to a profile file located at
"$BASH_IT_CUSTOM/profiles/*.bash_it".

How Has This Been Tested?

• I ran bash-it profile save to create a profile file.
• Moved it into my $BASH_IT_CUSTOM directory
• Linked that file into the $BASH_IT/profiles/ directory
• Tested loading and re-saving the profile after making changes

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.

[NoahGorny]

Thanks for contributing @punchagan !