Remove GLSLANG_ANGLE

ANGLE no longer links with glslang.  This change reverts
1ef2e250fc which added a flag to strip
glslang to reduce its binary size.  This flag is no longer needed.

BUILD.gn

@@ -96,9 +96,6 @@ action("glslang_extension_headers") {
 }
 
 spirv_tools_dir = glslang_spirv_tools_dir
-if (!defined(glslang_angle)) {
-  glslang_angle = false
-}
 
 config("glslang_public") {
   include_dirs = [ "." ]
@@ -242,9 +239,6 @@ template("glslang_sources_common") {
       sources += [ "SPIRV/SpvTools.cpp" ]
       defines += [ "ENABLE_OPT=1" ]
     }
-    if (invoker.is_angle) {
-      defines += [ "GLSLANG_ANGLE" ]
-    }
 
     if (is_win) {
       sources += [ "glslang/OSDependent/Windows/ossource.cpp" ]
@@ -293,15 +287,13 @@ template("glslang_sources_common") {
 }
 
 glslang_sources_common("glslang_lib_sources") {
-  enable_opt = !glslang_angle
-  enable_hlsl = !glslang_angle
-  is_angle = glslang_angle
+  enable_opt = true
+  enable_hlsl = true
 }
 
 glslang_sources_common("glslang_sources") {
   enable_opt = true
   enable_hlsl = true
-  is_angle = false
 }
 
 source_set("glslang_default_resource_limits_sources") {