build: drop unused variable replacement and comment

we're currently using boost 1.77, this replacement was dropped in its
patch form in bitcoin#19764 (backported as 6a367fc in dash#4356), the
comment was dropped in bitcoin#19761 but the change is in this commit
instead due to direct relevance.

Author: kwvg

depends/packages/boost.mk

@@ -39,10 +39,8 @@ $(package)_cxxflags_android=-fPIC
 $(package)_cxxflags_x86_64=-fcf-protection=full
 endef
 
-# Fix unused variable in boost_process, can be removed after upgrading to 1.72
 # Fix missing unary_function in clang15 on macos, can be removed after upgrading to 1.81
 define $(package)_preprocess_cmds
-  sed -i.old "s/int ret_sig = 0;//" boost/process/detail/posix/wait_group.hpp && \
   sed -i.old "s/unary_function/$(unary_function)/" boost/container_hash/hash.hpp && \
   echo "using $($(package)_toolset_$(host_os)) : : $($(package)_cxx) : <cflags>\"$($(package)_cflags)\" <cxxflags>\"$($(package)_cxxflags)\" <compileflags>\"$($(package)_cppflags)\" <linkflags>\"$($(package)_ldflags)\" <archiver>\"$($(package)_ar)\" <striper>\"$(host_STRIP)\"  <ranlib>\"$(host_RANLIB)\" <rc>\"$(host_WINDRES)\" : ;" > user-config.jam
 endef