Remove printing QR code using Google Charts URL

Google Charts URLs has been deprecated since 2012, and is finally
being turned off.

The remaining options for getting secrets into the app are:

1. Have `libqrencode` installed, generating a QR code locally and
   displaying it on the terminal.
2. Enter the secret manually via the text representation shown.

Fixes #244

src/google-authenticator.c

@@ -157,7 +157,7 @@ static const char *urlEncode(const char *s) {
 }
 
 static const char *getURL(const char *secret, const char *label,
-                          char **encoderURL, const int use_totp, const char *issuer) {
+                          const int use_totp, const char *issuer) {
   const char *encodedLabel = urlEncode(label);
   char *url;
   const char totp = use_totp ? 't' : 'h';
@@ -179,17 +179,6 @@ static const char *getURL(const char *secret, const char *label,
     url = newUrl;
   }
 
-  if (encoderURL) {
-    // Show a QR code.
-    const char *encoder = "https://www.google.com/chart?chs=200x200&"
-                          "chld=M|0&cht=qr&chl=";
-    const char *encodedURL = urlEncode(url);
-
-    *encoderURL = strcat(strcpy(malloc(strlen(encoder) +
-                                       strlen(encodedURL) + 1),
-                                encoder), encodedURL);
-    free((void *)encodedURL);
-  }
   free((void *)encodedLabel);
   return url;
 }
@@ -326,9 +315,7 @@ static void displayEnrollInfo(const char *secret, const char *label,
   if (qr_mode == QR_NONE) {
     return;
   }
-  char *encoderURL;
-  const char *url = getURL(secret, label, &encoderURL, use_totp, issuer);
-  printf("Warning: pasting the following URL into your browser exposes the OTP secret to Google:\n  %s\n", encoderURL);
+  const char *url = getURL(secret, label, use_totp, issuer);
 
   // Only newer systems have support for libqrencode. So instead of requiring
   // it at build-time we look for it at run-time. If it cannot be found, the
@@ -343,7 +330,6 @@ static void displayEnrollInfo(const char *secret, const char *label,
   }
 
   free((char *)url);
-  free(encoderURL);
 }
 
 // ask for a code. Return code, or some garbage if no number given. That's fine