Remove the "safemode" feature.

This feature has been designed with the sometimes quite flakey direct
(parallel or serial port attached) bitbang programming adapters in
mind that were quite common about two decades ago.

With parallel ports vanishing from modern PCs almost completely, and
the advent of various USB-attached low-cost programming devices,
this class of programmers disappeared almost completely.

Furthermore, the fuse combinations that were covered by the feature
are no longer around on all recent AVR devices, so for an ever
increasing number of devices, safemode already became meaningless and
was turned off anyway.

With the prospective version 7.x release, it's a good point in time to
introduce a major change like this one.

src/config_gram.y

@@ -77,7 +77,6 @@ static int pin_name;
 %token K_DEFAULT_BITCLOCK
 %token K_DEFAULT_PARALLEL
 %token K_DEFAULT_PROGRAMMER
-%token K_DEFAULT_SAFEMODE
 %token K_DEFAULT_SERIAL
 %token K_DESC
 %token K_FAMILY_ID
@@ -257,14 +256,6 @@ def :
   K_DEFAULT_BITCLOCK TKN_EQUAL number_real TKN_SEMI {
     default_bitclock = $3->value.number_real;
     free_token($3);
-  } |
-
-  K_DEFAULT_SAFEMODE TKN_EQUAL yesno TKN_SEMI {
-    if ($3->primary == K_YES)
-      default_safemode = 1;
-    else if ($3->primary == K_NO)
-      default_safemode = 0;
-    free_token($3);
   }
 ;