build: delete unused `REQUIRE_LIB_DEPS`

Unused since 97aca0971d #5808

Closes #14671

CMakeLists.txt

@@ -2036,8 +2036,6 @@ if(NOT CURL_DISABLE_INSTALL)
   else()
     set(ENABLE_STATIC       "no")
   endif()
-  # Set this to "yes" to append all libraries on which -lcurl is dependent
-  set(REQUIRE_LIB_DEPS "no")
 
   # Finally generate a "curl-config" matching this config.
   # Consumed variables:

configure.ac

@@ -503,12 +503,11 @@ AC_SUBST([LIBCURL_PC_CFLAGS])
 
 # Determine whether all dependent libraries must be specified when linking
 if test "X$enable_shared" = "Xyes" -a "X$link_all_deplibs" = "Xno"; then
-  REQUIRE_LIB_DEPS=no
+  require_lib_deps=no
 else
-  REQUIRE_LIB_DEPS=yes
+  require_lib_deps=yes
 fi
-AC_SUBST(REQUIRE_LIB_DEPS)
-AM_CONDITIONAL(USE_EXPLICIT_LIB_DEPS, test x$REQUIRE_LIB_DEPS = xyes)
+AM_CONDITIONAL(USE_EXPLICIT_LIB_DEPS, test x$require_lib_deps = xyes)
 
 dnl **********************************************************************
 dnl platform/compiler/architecture specific checks/flags