[libcxx] Remove the availability_markup LIT feature

It is now equivalent to the 'availability' LIT feature, so there's no
reason to keep both.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@348653 91177308-0d34-0410-b5e6-96231b3b80d8

docs/DesignDocs/AvailabilityMarkup.rst

@@ -55,7 +55,7 @@ or on a particular symbol:
 Testing
 =======
 
-Some parameters can be passed to lit to run the test-suite and exercising the
+Some parameters can be passed to lit to run the test-suite and exercise the
 availability.
 
 * The `platform` parameter controls the deployment target. For example lit can
@@ -69,8 +69,7 @@ availability.
 Tests can be marked as XFAIL based on multiple features made available by lit:
 
 
-* if `use_system_cxx_lib` is passed to lit, assuming `--param=platform=macosx10.8`
-  is passed as well the following features will be available:
+* if `--param=platform=macosx10.8` is passed, the following features will be available:
 
   - availability
   - availability=x86_64
@@ -82,8 +81,8 @@ Tests can be marked as XFAIL based on multiple features made available by lit:
   This feature is used to XFAIL a test that *is* using a class or a method marked
   as unavailable *and* that is expected to *fail* if deployed on an older system.
 
-* if `use_system_cxx_lib` is passed to lit, the following features will also
-  be available:
+* if `use_system_cxx_lib` and `--param=platform=macosx10.8` are passed to lit,
+  the following features will also be available:
 
   - with_system_cxx_lib
   - with_system_cxx_lib=x86_64
@@ -94,19 +93,7 @@ Tests can be marked as XFAIL based on multiple features made available by lit:
 
   This feature is used to XFAIL a test that is *not* using a class or a method
   marked as unavailable *but* that is expected to fail if deployed on an older
-  system. For example if we know that it exhibits a bug in the libc on a
-  particular system version.
-
-* if `with_availability` is passed to lit, the following features will also
-  be available:
-
-  - availability_markup
-  - availability_markup=x86_64
-  - availability_markup=macosx
-  - availability_markup=x86_64-macosx
-  - availability_markup=x86_64-apple-macosx10.8
-  - availability_markup=macosx10.8
-
-  This feature is used to XFAIL a test that *is* using a class or a method
-  marked as unavailable *but* that is expected to *pass* if deployed on an older
-  system. For example if it is using a symbol in a statically evaluated context.
+  system. For example, if the test exhibits a bug in the libc on a particular
+  system version, or if the test uses a symbol that is not available on an
+  older version of the dylib (but for which there is no availability markup,
+  otherwise the XFAIL should use `availability` above).