Remove "fastcomp-master" SDKs from emsdk_manifest.json (#752)

It makes not sense to install fastcomp with the current main
branch of binaryen and emscripten so remove these SDK options.
diff --git a/emsdk_manifest.json b/emsdk_manifest.json
index 1a2a687..b522c02 100644
--- a/emsdk_manifest.json
+++ b/emsdk_manifest.json
@@ -486,36 +486,6 @@
     "os": "linux"
   },
   {
-    "version": "fastcomp-master",
-    "bitness": 32,
-    "uses": ["fastcomp-clang-master-32bit", "node-14.15.5-32bit", "python-3.7.4-32bit", "java-8.152-32bit", "emscripten-main-32bit", "binaryen-main-32bit"],
-    "os": "win"
-  },
-  {
-    "version": "fastcomp-master",
-    "bitness": 64,
-    "uses": ["fastcomp-clang-master-64bit", "node-14.15.5-64bit", "python-3.7.4-pywin32-64bit", "java-8.152-64bit", "emscripten-main-64bit", "binaryen-main-64bit"],
-    "os": "win"
-  },
-  {
-    "version": "fastcomp-master",
-    "bitness": 64,
-    "uses": ["fastcomp-clang-master-64bit", "node-14.15.5-64bit", "python-3.7.4-2-64bit", "emscripten-main-64bit", "binaryen-main-64bit"],
-    "os": "macos"
-  },
-  {
-    "version": "fastcomp-master",
-    "bitness": 32,
-    "uses": ["fastcomp-clang-master-32bit", "node-14.15.5-32bit", "emscripten-main-32bit", "binaryen-main-32bit"],
-    "os": "linux"
-  },
-  {
-    "version": "fastcomp-master",
-    "bitness": 64,
-    "uses": ["fastcomp-clang-master-64bit", "node-14.15.5-64bit", "emscripten-main-64bit", "binaryen-main-64bit"],
-    "os": "linux"
-  },
-  {
     "version": "fastcomp-tag-%tag%",
     "bitness": 32,
     "uses": ["fastcomp-clang-tag-e%tag%-32bit", "node-8.9.1-32bit", "python-2.7.13.1-32bit", "java-8.152-32bit", "emscripten-tag-%tag%-32bit", "binaryen-tag-%tag%-32bit"],