Revert "Show how fish was executed, using argv[0] for program_name"

This reverts commit 1cb8b2a87b.

argv[0] has the full path in it for a user when he executes it
out of $PATH. This is really annoying in the title which uses $_.

src/fish_key_reader.cpp

@@ -383,7 +383,7 @@ static bool parse_flags(int argc, char **argv, bool *continuous_mode) {
 }
 
 int main(int argc, char **argv) {
-    program_name = argv[0];
+    program_name = L"fish_key_reader";
     bool continuous_mode = false;
 
     if (!parse_flags(argc, argv, &continuous_mode)) return 1;