Remove the revision and unpin the manifest.

Test: N/A
Change-Id: I637b28cf84acb65c70e3d0340aff6cfa2f2a071f
diff --git a/default.xml b/default.xml
index 090ab77..a4840a0 100644
--- a/default.xml
+++ b/default.xml
@@ -43,8 +43,8 @@
 
   <!-- prebuilts projects -->
   <project path="prebuilts/build-tools" name="platform/prebuilts/build-tools" clone-depth="1" />
-  <project path="prebuilts/clang/host/darwin-x86" name="platform/prebuilts/clang/host/darwin-x86" clone-depth="1" revision="fb2687e4347d45e17a68edca0eb52b29b6da775d" />
-  <project path="prebuilts/clang/host/linux-x86" name="platform/prebuilts/clang/host/linux-x86" clone-depth="1" revision="ee941ede0f2be22ece1ba3a22ce553f6973e469b" />
+  <project path="prebuilts/clang/host/darwin-x86" name="platform/prebuilts/clang/host/darwin-x86" clone-depth="1" />
+  <project path="prebuilts/clang/host/linux-x86" name="platform/prebuilts/clang/host/linux-x86" clone-depth="1" />
   <project path="prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8" name="platform/prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8" clone-depth="1" revision="d9aafaade740ca38612c742f6d87debf362132ea" />
   <project path="prebuilts/jdk/jdk8" name="platform/prebuilts/jdk/jdk8" clone-depth="1" />
   <project path="prebuilts/jdk/jdk9" name="platform/prebuilts/jdk/jdk9" clone-depth="1" />