util: change GetWarnings parameter to bool

GetWarnings() changes the format of the output warning string based on a
passed-in string argument that can be set to "gui" or "statusbar".
Change the argument to a bool:

- there are only two types of behaviour, so a bool is a more natural
argument type
- changing the name to 'verbose' does not set any expectations for the
how the calling code will use the returned string (currently,
'statusbar' is used for RPC warnings, not a status bar)
- removes some error-handling code for when the passed-in string is not
one of the two strings expected.

src/warnings.h

@@ -13,11 +13,11 @@ void SetfLargeWorkForkFound(bool flag);
 bool GetfLargeWorkForkFound();
 void SetfLargeWorkInvalidChainFound(bool flag);
 /** Format a string that describes several potential problems detected by the core.
- * @param[in] strFor can have the following values:
- * - "statusbar": get the most important warning
- * - "gui": get all warnings, translated (where possible) for GUI, separated by <hr />
- * @returns the warning string selected by strFor
+ * @param[in] verbose bool
+ * - if true, get all warnings, translated (where possible), separated by <hr />
+ * - if false, get the most important warning
+ * @returns the warning string
  */
-std::string GetWarnings(const std::string& strFor);
+std::string GetWarnings(bool verbose);
 
 #endif //  BITCOIN_WARNINGS_H