[lldb] s/ExecutionContext/Target in Disassembler

Some functions in this file only use the "target" component of an
execution context. Adjust the argument lists to reflect that.

This avoids some defensive null checks and simplifies most of the
callers.

lldb/source/Target/ThreadPlanStepRange.cpp

@@ -264,12 +264,11 @@ InstructionList *ThreadPlanStepRange::GetInstructionsForAddress(
 
       if (!m_instruction_ranges[i]) {
         // Disassemble the address range given:
-        ExecutionContext exe_ctx(m_thread.GetProcess());
         const char *plugin_name = nullptr;
         const char *flavor = nullptr;
         const bool prefer_file_cache = true;
         m_instruction_ranges[i] = Disassembler::DisassembleRange(
-            GetTarget().GetArchitecture(), plugin_name, flavor, exe_ctx,
+            GetTarget().GetArchitecture(), plugin_name, flavor, GetTarget(),
             m_address_ranges[i], prefer_file_cache);
       }
       if (!m_instruction_ranges[i])