scripted-diff: Fix references to share/rpcuser (now share/rpcauth)

Commit 3fdb29778a renamed share/rpcuser to share/rpcauth but left references to the old path in code; this commit fixes the old references.

Performed update using https://github.com/facebook/codemod with command: `codemod --extensions cpp,py,md 'share/rpcuser' 'share/rpcauth'`

-BEGIN VERIFY SCRIPT-
git grep --files-with-matches 'share/rpcuser' src/*.cpp | xargs sed -i -E 's:share/rpcuser:share/rpcauth:g'
git grep --files-with-matches 'share/rpcuser' test/functional/*.py | xargs sed -i -E 's:share/rpcuser:share/rpcauth:g'
-END VERIFY SCRIPT-

test/functional/rpc_users.py

@@ -59,7 +59,7 @@ class HTTPBasicsTest(BitcoinTestFramework):
         #Old authpair
         authpair = url.username + ':' + url.password
 
-        #New authpair generated via share/rpcuser tool
+        #New authpair generated via share/rpcauth tool
         password = "cA773lm788buwYe4g4WT+05pKyNruVKjQ25x3n0DQcM="
 
         #Second authpair with different username