Remove redundant .c_str()s

After the tinyformat switch sprintf() family functions support passing
actual std::string objects.

Remove unnecessary c_str calls (236 of them) in logging and formatting.

src/alert.cpp

@@ -69,18 +69,18 @@ std::string CUnsignedAlert::ToString() const
         nExpiration,
         nID,
         nCancel,
-        strSetCancel.c_str(),
+        strSetCancel,
         nMinVer,
         nMaxVer,
-        strSetSubVer.c_str(),
+        strSetSubVer,
         nPriority,
-        strComment.c_str(),
-        strStatusBar.c_str());
+        strComment,
+        strStatusBar);
 }
 
 void CUnsignedAlert::print() const
 {
-    LogPrintf("%s", ToString().c_str());
+    LogPrintf("%s", ToString());
 }
 
 void CAlert::SetNull()