Delete dead code

[gabrielbornstein]

This MR deletes dead code.

The total code audited includes:
- stable_string_store
- lru_clock
- sha256
- crc
- fuse stuff
- llfs_fuse/
- worker_task
- inode
- file_log_driver.*
- file_segment_ref.*
- filesystem_page_device.*
- old TurtleDB snapshot stuff
- packed_log_page_header.* ?
- raw_volume_log_data_parser
- trie (once packed art / blocked leaf pages are merged)
- old LogDevice (pre ioring_logdevice2)
- llfs_cli/*

The code that was NOT deleted includes:
- trie (dependent code not merged yet)
- packed_log_page_header.* ? (still seems to be in use)
- raw_volume_log_data_parser (still seems to be in use)
- old LogDevice (appeared to already have been deleted)
- file_segment_ref (still seems to be in use)

These deletions improve line code coverage from 67% to 74%.

NOTE: When testing locally, the following test failed when building with coverage flags, but passed without them:

[ RUN      ] RingBufferTest.PoolIndex
/home/gbornste/Projects/mps/llfs/src/llfs/ring_buffer.test.cpp:124: Failure
Expected equality of these values:
  index0
    Which is: 864
  (63 << 4)
    Which is: 1008
 std::bitset<16>{index0} == 0000001101100000

[  FAILED  ] RingBufferTest.PoolIndex (3163 ms)