fix deprecated warning with DelByName. lock is already taken

[heitbaum]

fixes:

connectionVTP.c: In member function 'bool cConnectionVTP::CmdDELR(const char*)': connectionVTP.c:2036:70: warning: 'void cRecordings::DelByName(const char*)' is deprecated: use explicit locking, deleting etc. [-Wdeprecated-declarations]
 2036 |                                                 Recordings->DelByName(recording->FileName());
      |                                                 ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
In file included from /var/media/DATA/home-rudi/LibreELEC.tv/build.LibreELEC-Generic.x86_64-13.0-devel/build/vdr-2.8.1/skins.h:18,
                 from /var/media/DATA/home-rudi/LibreELEC.tv/build.LibreELEC-Generic.x86_64-13.0-devel/build/vdr-2.8.1/osdbase.h:15,
                 from /var/media/DATA/home-rudi/LibreELEC.tv/build.LibreELEC-Generic.x86_64-13.0-devel/build/vdr-2.8.1/menuitems.h:15,
                 from /var/media/DATA/home-rudi/LibreELEC.tv/build.LibreELEC-Generic.x86_64-13.0-devel/build/vdr-2.8.1/plugin.h:14,
                 from ../common.h:15,
                 from ../server/connection.h:9,
                 from ../server/connectionVTP.h:4,
                 from connectionVTP.c:5:
/var/media/DATA/home-rudi/LibreELEC.tv/build.LibreELEC-Generic.x86_64-13.0-devel/build/vdr-2.8.1/recording.h:314:62: note: declared here
  314 |   [[deprecated("use explicit locking, deleting etc.")]] void DelByName(const char *FileName);
      |                                                              ^~~~~~~~~

[M-Reimer]

I had a look at how VDR handles recording deletion:
vdr-projects/vdr@63abb60
Would it be a good idea to add your change in a new version check and also add the recording to "DeletedRecordings"?