build: cmake: do not add "absl::headers" to include dirs

`absl::headers` is a library, not the path to its headers.

before this change, the command lines of genereated build rule look
like:

```
-I/home/kefu/dev/scylladb/repair/absl::headers
```

this does not hurt, as other libraries might add the intended include
dir to the compiler command line, but this is just wrong.

so let's remove it. please note, `repair` target already links against
`absl::headers`. so we don't need to add `absl::headers` to its linkage
again.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes scylladb/scylladb#19384

repair/CMakeLists.txt

@@ -6,7 +6,6 @@ target_sources(repair
     table_check.cc)
 target_include_directories(repair
   PUBLIC
-    absl::headers
     ${CMAKE_SOURCE_DIR})
 target_link_libraries(repair
   PUBLIC