Fix E2_AGENT linking w.r.t. simulators

Link E2_AGENT libraries directly into nr-softmodem/lte-softmodem instead
of L2/L2_NR/F1AP. Doing that ensures that simulators, e.g.,
nr_dlsim/nr_ulsim do still compile. It also simplifies the code.

Prior to this, compiling nr_ulsim with E2_AGENT, for instance, resulted
in the following errors, fixed in this commit:

    FAILED: nr_ulsim
    /usr/bin/ld: openair2/E2AP/RAN_FUNCTION/libe2_ran_func_du_cucp_cuup.a(ran_func_rc.c.o): in function `send_aper_ric_ind':
    /home/oai/robert/cleanup-t-dependency-cmake/openair2/E2AP/RAN_FUNCTION/O-RAN/ran_func_rc.c:643: (.text+0xee6): undefined reference to `async_event_agent_api'
    /usr/bin/ld: /home/oai/robert/cleanup-t-dependency-cmake/openair2/E2AP/RAN_FUNCTION/O-RAN/ran_func_rc.c:643:(.text+0x11ca): undefined reference to `async_event_agent_api'
    /usr/bin/ld: /home/oai/robert/cleanup-t-dependency-cmake/openair2/E2AP/RAN_FUNCTION/O-RAN/ran_func_rc.c:643:(.text+0x1485): undefined reference to `async_event_agent_api'
    /usr/bin/ld: /home/oai/robert/cleanup-t-dependency-cmake/openair2/E2AP/RAN_FUNCTION/O-RAN/ran_func_rc.c:643:(.text+0x159c): undefined reference to `async_event_agent_api'
    /usr/bin/ld: /home/oai/robert/cleanup-t-dependency-cmake/openair2/E2AP/RAN_FUNCTION/O-RAN/ran_func_rc.c:643:(.text+0x16b1): undefined reference to `async_event_agent_api'
    [...]

CMakeLists.txt

@@ -464,9 +464,6 @@ target_include_directories(f1ap PUBLIC F1AP_DIR)
 target_link_libraries(f1ap PUBLIC asn1_f1ap GTPV1U)
 target_link_libraries(f1ap PRIVATE ngap nr_rrc HASHTABLE f1ap_lib)
 target_include_directories(f1ap PRIVATE ${F1AP_DIR}/lib)
-if(E2_AGENT)
-  target_compile_definitions(f1ap PRIVATE E2_AGENT)
-endif()
 
 # LPP
 ##############
@@ -1306,12 +1303,6 @@ add_library(L2
 target_link_libraries(L2 PRIVATE x2ap s1ap lte_rrc m2ap)
 target_link_libraries(L2 PRIVATE asn1_lte_rrc_hdrs asn1_nr_rrc_hdrs)
 
-if(E2_AGENT)
-  target_link_libraries(L2 PUBLIC e2_agent e2_agent_arg e2_ran_func_du_cucp_cuup)
-  target_compile_definitions(L2 PRIVATE ${E2AP_VERSION} ${KPM_VERSION} E2_AGENT)
-endif()
-
-
 add_library(MAC_UE_NR ${MAC_NR_SRC_UE})
 target_link_libraries(MAC_UE_NR PRIVATE asn1_lte_rrc_hdrs asn1_nr_rrc_hdrs PUBLIC nr_ue_power_procedures nr_ue_ra_procedures)
 
@@ -1338,10 +1329,6 @@ target_link_libraries(L2_NR PRIVATE f1ap x2ap s1ap ngap nr_rrc e1ap nr_rlc nr_co
 if(OAI_AERIAL)
     target_compile_definitions(L2_NR PRIVATE ENABLE_AERIAL)
 endif()
-if(E2_AGENT)
-  target_link_libraries(L2_NR PUBLIC e2_agent e2_agent_arg e2_ran_func_du_cucp_cuup)
-  target_compile_definitions(L2_NR PRIVATE ${E2AP_VERSION} ${KPM_VERSION} E2_AGENT)
-endif()
 
 add_library(L2_LTE_NR
   # temporary solution until 4G/5G code completely untangled (as evidenced by deletion of the following file)
@@ -1754,6 +1741,7 @@ target_link_libraries(lte-softmodem PRIVATE asn1_nr_rrc_hdrs asn1_lte_rrc_hdrs)
 target_link_libraries(lte-softmodem PRIVATE ${blas_LIBRARIES} ${cblas_LIBRARIES} ${lapacke_LIBRARIES} ${lapack_LIBRARIES})
 
 if(E2_AGENT)
+  target_link_libraries(lte-softmodem PUBLIC e2_agent e2_agent_arg e2_ran_func_du_cucp_cuup)
   target_compile_definitions(lte-softmodem PRIVATE ${E2AP_VERSION} ${KPM_VERSION} E2_AGENT)
 endif()
 
@@ -1857,6 +1845,7 @@ if (OAI_AERIAL)
   target_link_libraries(nr-softmodem PUBLIC aerial_lib)
 endif()
 if(E2_AGENT)
+  target_link_libraries(nr-softmodem PUBLIC e2_agent e2_agent_arg e2_ran_func_du_cucp_cuup)
   target_compile_definitions(nr-softmodem PRIVATE ${E2AP_VERSION} ${KPM_VERSION} E2_AGENT)
 endif()