cmake: remove the separate folly_symbolizer library target

Summary:
The code in folly/experimental/symbolizer/* is already included in the main
libfolly library if it is supported by the build configuration.  Remove the
separate libfolly_symbolizer target added in D9216312 that includes a second
copy of these objects.

This change effectively reverts D9216312.

Reviewed By: Orvid, calebmarchent

Differential Revision: D9229946

fbshipit-source-id: d8e6874eeab8c9c1aa519441bd29ae107aef03ac

folly/CMakeLists.txt

@@ -13,4 +13,3 @@ install(
 )
 
 add_subdirectory(experimental/exception_tracer)
-add_subdirectory(experimental/symbolizer)

folly/experimental/symbolizer/CMakeLists.txt

-if (FOLLY_USE_SYMBOLIZER)
-  file(GLOB files *.cpp)
-  add_library(
-    folly_symbolizer
-    ${files}
-  )
-  apply_folly_compile_options_to_target(folly_symbolizer)
-  target_link_libraries(
-    folly_symbolizer
-    PUBLIC folly
-  )
-endif()