[libcxx][NFC] removes BreakBeforeConceptDeclarations from .clang-format

BreakBeforeConceptDeclarations is apparently breaking CI.

Partially rolls back 2e3a78b8ca10.

GitOrigin-RevId: ff0ada4e1607385be30b2b38885cea2127568e04
diff --git a/.clang-format b/.clang-format
index bef1d9d..bdd9ef0 100644
--- a/.clang-format
+++ b/.clang-format
@@ -15,6 +15,5 @@
 ColumnLimit: 120
 
 # These aren't covered by the LLVM Style Guide
-BreakBeforeConceptDeclarations: true
 IndentRequires: false
 ---