[ADT] Remove StringRef::{startswith,endswith} (#89548)

These functions have been deprecated since:

  commit 5ac1295
  Author: Kazu Hirata <[email protected]>
  Date:   Sun Dec 17 15:52:50 2023 -0800

Author: kazutakahirata

llvm/include/llvm/ADT/StringRef.h

@@ -263,11 +263,6 @@ namespace llvm {
       return Length >= Prefix.Length &&
              compareMemory(Data, Prefix.Data, Prefix.Length) == 0;
     }
-    [[nodiscard]] LLVM_DEPRECATED(
-        "Use starts_with instead",
-        "starts_with") bool startswith(StringRef Prefix) const {
-      return starts_with(Prefix);
-    }
     [[nodiscard]] bool starts_with(char Prefix) const {
       return !empty() && front() == Prefix;
     }
@@ -281,11 +276,6 @@ namespace llvm {
              compareMemory(end() - Suffix.Length, Suffix.Data, Suffix.Length) ==
                  0;
     }
-    [[nodiscard]] LLVM_DEPRECATED(
-        "Use ends_with instead",
-        "ends_with") bool endswith(StringRef Suffix) const {
-      return ends_with(Suffix);
-    }
     [[nodiscard]] bool ends_with(char Suffix) const {
       return !empty() && back() == Suffix;
     }