Revert "[Sema] Enable require explicit availability by default for public modules"

This reverts commit 2175e4e.

Author: xymus

lib/Frontend/CompilerInvocation.cpp

@@ -729,8 +729,7 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
                      diagLevel);
     }
   } else if (Args.getLastArg(OPT_require_explicit_availability,
-                             OPT_require_explicit_availability_target) ||
-             Opts.LibraryLevel == LibraryLevel::API) {
+                             OPT_require_explicit_availability_target)) {
     Opts.RequireExplicitAvailability = DiagnosticBehavior::Warning;
   }
 

test/attr/require_explicit_availability.swift

@@ -10,17 +10,6 @@
 // RUN:   -target %target-cpu-apple-macosx10.10 -require-explicit-availability=warn \
 // RUN:   -require-explicit-availability-target "macOS 10.10"
 
-/// Using -library-level api defaults to enabling warnings, without fixits.
-// RUN: sed -e "s/}} {{.*/}}/" < %s > %t/NoFixits.swift
-// RUN: %target-swift-frontend -typecheck -parse-as-library -verify %t/NoFixits.swift \
-// RUN:   -target %target-cpu-apple-macosx10.10 -library-level api
-
-/// Explicitly disable the diagnostic.
-// RUN: sed -e 's/xpected-warning/not-something-expected/' < %s > %t/None.swift
-// RUN: %target-swift-frontend -typecheck -parse-as-library -verify %t/None.swift \
-// RUN:   -target %target-cpu-apple-macosx10.10 -require-explicit-availability=ignore \
-// RUN:   -require-explicit-availability-target "macOS 10.10" -library-level api
-
 /// Upgrade the diagnostic to an error.
 // RUN: sed -e "s/xpected-warning/xpected-error/" < %s > %t/Errors.swift
 // RUN: %target-swift-frontend -typecheck -parse-as-library -verify %t/Errors.swift \