This should work:
text = text.replaceAll("(?m)^[*:#]+\\s*", "");
Important is using (?m)
for MULTILINE
mode here that lets you use line start/end anchors for each line.
OUTPUT:
definition list
some list item
another list item
[[Category:1918 births]]
[[Category:2005 deaths]]
[[Category:Scottish female singers]]
[[Category:Billy Cotton Band Show]]
[[Category:Deaths from Alzheimer's disease]]
[[Category:People from Glasgow]]