os: remove catch-all from FS VFS update mtime

Only 'alloc_packet' is supposed to throw an exception, which is already
caught. The 'submit_packet' call does not need further handling.

Issue #3713.

repos/os/src/lib/vfs/fs_file_system.h

@@ -289,9 +289,6 @@ class Vfs::Fs_file_system : public File_system
 					source.submit_packet(p);
 				} catch (::File_system::Session::Tx::Source::Packet_alloc_failed) {
 					return false;
-				} catch (...) {
-					Genode::error("unhandled exception");
-					return false;
 				}
 
 				return true;