Remove questionable asserts

Both osl_add/removeSignalHandler apparently handle !handler gracefully (the
former even including explicit code for that case, which doesn't fit with having
an assert), and before bca760c2 "tdf#43157 -
osl: convert OSL_ASSERTs to assert in signalshared.cxx" those asserts were
merely OSL_ASSERTs.  So keep this published API accepting !handler (even if the
documentation is silent on this).

Change-Id: I63512916a66a2a58b932174ec5d92ce612c236a2

sal/osl/all/signalshared.cxx

@@ -17,7 +17,6 @@
  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  */
 
-#include <cassert>
 #include <sal/config.h>
 
 #include <signalshared.hxx>
@@ -68,8 +67,6 @@ oslSignalAction callSignalHandler(oslSignalInfo* pInfo)
 
 oslSignalHandler SAL_CALL osl_addSignalHandler(oslSignalHandlerFunction handler, void* pData)
 {
-    assert(handler);
-
     if (!handler)
         return nullptr;
 
@@ -98,8 +95,6 @@ oslSignalHandler SAL_CALL osl_addSignalHandler(oslSignalHandlerFunction handler,
 
 sal_Bool SAL_CALL osl_removeSignalHandler(oslSignalHandler handler)
 {
-    assert(handler);
-
     if (!bInitSignal)
         bInitSignal = initSignal();