scripted-diff: Rename PROVIDE_MAIN_FUNCTION -> PROVIDE_FUZZ_MAIN_FUNCTION

Summary:

-BEGIN VERIFY SCRIPT-
sed -i -e 's/PROVIDE_MAIN_FUNCTION/PROVIDE_FUZZ_MAIN_FUNCTION/g' $(git grep -l PROVIDE_MAIN_FUNCTION)
-END VERIFY SCRIPT-

This is a partial backport of core#21264
https://github.com/bitcoin/bitcoin/pull/21264/commits/fa4fbec03e4395a6ab75ea98a696bee6d768e97e

Test Plan: ninja bitcoin-fuzzers

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15307