MT#7335 Fix flex issues when compiling for Debian/jessie

Fixes:

| conf_lex.c:618:11: error: conflicting types for 'yyget_leng'
| yy_size_t yyget_leng (void );
| ^
| conf_lex.l:55:5: note: previous declaration of 'yyget_leng' was here

flex-2.5.35 used to declare:

  int yyget_leng (void );

while flex-2.5.39 uses:

  yy_size_t yyget_leng (void );

nowadays. We're build-depending on flex anyway so there's no point
in declaring that in heartbeat's source again. (And upstream dropped
dropped that code in recent versions as well.)

Also drop automatically generated telecom/recoverymgrd/conf_lex.c,
this adds more confusion than benefit otherwise.