Simplify users of StringRef::{l,r}trim (NFC)

r260925 introduced a version of the *trim methods which is preferable
when trimming a single kind of character. Update all users in llvm.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@260926 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/YAMLParser.cpp

@@ -1911,7 +1911,7 @@ StringRef ScalarNode::getValue(SmallVectorImpl<char> &Storage) const {
     return UnquotedValue;
   }
   // Plain or block.
-  return Value.rtrim(" ");
+  return Value.rtrim(' ');
 }
 
 StringRef ScalarNode::unescapeDoubleQuoted( StringRef UnquotedValue