Fix typo: ENCODE_BY_LITTEL_ENDIAN → ENCODE_BY_LITTLE_ENDIAN (#825)

* Initial plan

* Fix typo: ENCODE_BY_LITTEL_ENDIAN → ENCODE_BY_LITTLE_ENDIAN

Agent-Logs-Url: https://github.com/ithewei/libhv/sessions/8e4ecff3-c8d8-43af-b29d-336c92e28c28

Co-authored-by: ithewei <26049660+ithewei@users.noreply.github.com>

* Remove backward compatibility for little endian encoding

Removed backward compatibility definition for ENCODE_BY_LITTEL_ENDIAN.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ithewei <26049660+ithewei@users.noreply.github.com>
Co-authored-by: ithewei <ithewei@163.com>

Author: Copilot

event/hloop.h

@@ -497,7 +497,7 @@ typedef enum {
 // UNPACK_BY_LENGTH_FIELD
 typedef enum {
     ENCODE_BY_VARINT        = 17,               // 1 MSB + 7 bits
-    ENCODE_BY_LITTEL_ENDIAN = LITTLE_ENDIAN,    // 1234
+    ENCODE_BY_LITTLE_ENDIAN = LITTLE_ENDIAN,    // 1234
     ENCODE_BY_BIG_ENDIAN    = BIG_ENDIAN,       // 4321
     ENCODE_BY_ASN1          = 80,               // asn1 decode int
 } unpack_coding_e;