[gn bulid] Remove phantom WebAssembly tablegen() calls

Apparenlty I added these in https://reviews.llvm.org/rL350628 but
I'm not sure why. They never existed in the CMake build, and now
they're causing trouble.

llvm/utils/gn/secondary/llvm/lib/Target/WebAssembly/BUILD.gn

@@ -1,11 +1,5 @@
 import("//llvm/utils/TableGen/tablegen.gni")
 
-tablegen("WebAssemblyGenCallingConv") {
-  visibility = [ ":LLVMWebAssemblyCodeGen" ]
-  args = [ "-gen-callingconv" ]
-  td_file = "WebAssembly.td"
-}
-
 tablegen("WebAssemblyGenDAGISel") {
   visibility = [ ":LLVMWebAssemblyCodeGen" ]
   args = [ "-gen-dag-isel" ]
@@ -18,32 +12,10 @@ tablegen("WebAssemblyGenFastISel") {
   td_file = "WebAssembly.td"
 }
 
-tablegen("WebAssemblyGenGlobalISel") {
-  visibility = [ ":LLVMWebAssemblyCodeGen" ]
-  args = [ "-gen-global-isel" ]
-  td_file = "WebAssembly.td"
-}
-
-tablegen("WebAssemblyGenMCPseudoLowering") {
-  visibility = [ ":LLVMWebAssemblyCodeGen" ]
-  args = [ "-gen-pseudo-lowering" ]
-  td_file = "WebAssembly.td"
-}
-
-tablegen("WebAssemblyGenRegisterBank") {
-  visibility = [ ":LLVMWebAssemblyCodeGen" ]
-  args = [ "-gen-register-bank" ]
-  td_file = "WebAssembly.td"
-}
-
 static_library("LLVMWebAssemblyCodeGen") {
   deps = [
-    ":WebAssemblyGenCallingConv",
     ":WebAssemblyGenDAGISel",
     ":WebAssemblyGenFastISel",
-    ":WebAssemblyGenGlobalISel",
-    ":WebAssemblyGenMCPseudoLowering",
-    ":WebAssemblyGenRegisterBank",
     "MCTargetDesc",
     "TargetInfo",
     "//llvm/include/llvm/Config:llvm-config",