cmake_transform_depfile: Remove unused incomplete vstlog support
In !5325 (merged) a partial implementation for converting MSBuild "TLog" format files was added. However, it is unused and incomplete:
- Does not enforce absolute paths as TLog docs require.
- Does not upper-case paths as TLog docs recommend.
- The TLog format semantics are not equivalent to
out: in
.
Remove the unused TLog transform infrastructure to avoid confusion.
Issue: #20286 (closed)