Update hourly salary calculation

[niraj2477]

Description

This PR refactors the hourly salary calculation logic across the codebase to use a common method that accounts for each employee's work schedule. It also removes an unused custom field from the Employee DocType.

Relevant Technical Choices

• Update common method to work based on the employee schedule.

Testing Instructions

Additional Information:

Screenshot/Screencast

Checklist

• I have carefully reviewed the code before submitting it for review.
• This code is adequately covered by unit tests to validate its functionality.
• I have conducted thorough testing to ensure it functions as intended.
• A member of the QA team has reviewed and tested this PR (To be checked by QA or code reviewer)