"""Removes all lines within and including the SEMANTIC INDEX section from the input content.

This function processes a multi-line string and removes any lines that are part of a SEMANTIC INDEX section. 
A SEMANTIC INDEX section is identified by a line starting with '## SEMANTIC INDEX'. The section continues until 
the next line that starts with '##' but is not '## SEMANTIC INDEX'. The function preserves all other lines 
outside of these sections.

Args:
    content (str): The input string containing the content to be processed.

Returns:
    str: The processed string with all SEMANTIC INDEX sections removed.

Note:
    - If the input content contains multiple SEMANTIC INDEX sections, all of them will be removed.
    - Lines outside of SEMANTIC INDEX sections are preserved in their original order.
"""