[dotnet] Stop adding the LICENSE file twice to the manifest pack.

Fixes this warning:

> warning NU5118: File 'xamarin-macios/LICENSE' is not added because the package already contains file '/LICENSE'

dotnet/.gitignore

@@ -1,5 +1,4 @@
 tmpdir
-Workloads/Microsoft.NET.Sdk.*/LICENSE
 WorkloadManifest.json
 WorkloadManifest.targets
 nupkgs

dotnet/Makefile

@@ -194,16 +194,12 @@ Workloads/Microsoft.NET.Sdk.$(1)/WorkloadManifest.targets: Makefile $(TOP)/Make.
 	$$(Q_GEN) $(GENERATE_WORKLOADMANIFEST_TARGETS_EXEC) "$(1)" "$$@.tmp" "$$(DOTNET_WINDOWS_PLATFORMS)" "$(DOTNET_TFM)_$$($(4)_NUGET_OS_VERSION)" "$(SUPPORTED_API_VERSIONS_$(4))"
 	$$(Q) mv $$@.tmp $$@
 
-Workloads/Microsoft.NET.Sdk.$(1)/LICENSE: $(TOP)/LICENSE | Workloads/Microsoft.NET.Sdk.$(1)
-	$$(Q) $(CP) $$< $$@
 
 WORKLOAD_TARGETS += Workloads/Microsoft.NET.Sdk.$(1)/WorkloadManifest.json
 WORKLOAD_TARGETS += Workloads/Microsoft.NET.Sdk.$(1)/WorkloadManifest.targets
-WORKLOAD_TARGETS += Workloads/Microsoft.NET.Sdk.$(1)/LICENSE
 
 LOCAL_WORKLOAD_TARGETS += Workloads/Microsoft.NET.Sdk.$(1)/WorkloadManifest.json
 LOCAL_WORKLOAD_TARGETS += Workloads/Microsoft.NET.Sdk.$(1)/WorkloadManifest.targets
-LOCAL_WORKLOAD_TARGETS += Workloads/Microsoft.NET.Sdk.$(1)/LICENSE
 endef
 $(foreach platform,$(DOTNET_PLATFORMS),$(eval $(call WorkloadTargets,$(platform),$(shell echo $(platform) | tr A-Z a-z),$($(platform)_NUGET_VERSION_NO_METADATA),$(shell echo $(platform) | tr a-z A-Z),$(NET8_$(platform)_NUGET_VERSION_NO_METADATA))))