Remove mixed-source.patch from zlib.

third_party/zlib/README.chromium

 Name: zlib
 URL: http://zlib.net/
 Version: 1.2.8
 Security Critical: yes
 License: Custom license
 License Android Compatible: yes
 
 Description:
 General purpose compression library
 
 Local Modifications:
 A few minor changes, all marked with "Google":
 - Added #ifdefs to avoid compile warnings when NO_GZCOMPRESS is defined.
 - Removed use of strerror for WinCE in gzio.c.
 - Added 'int z_errno' global for WinCE, to which 'errno' is defined in zutil.h.
 - Added 'mozzconf.h' to mangle the function names.
 - Added logic in zlib.h to undef our earlier mangles when defaulting to 64 bit offset versions of API.
 - Added casts to suppress VC++ warnings
 The 'google.patch' file represents our changes from the original zlib-1.2.5.
 
-A more significant change to support mixed-source data compression. See
-crbug.com/139744 and mixed-source.patch.
-
 Integrated Intel SIMD optimisations from: https://github.com/jtkukunas/zlib/
 and modified to accomodate the older version and existing changes in tree.
 
 This introduces new files: simd_stub.c, crc_folding.c, fill_window_sse.c and
 x86.[ch]. All but the latter are built into a static library to allow the
 compiler to use the desired instructions only when valid. The latter version is
 only built on x86 (32-bit and 64-bit) systems with it's functionality stubbed
 on the others.
 
 Other changes to accomodate:
 - fill_window() implementation calls into _sse() variant when supported and the
   original implementation renamed to _c()
 - read_buf was moved from local to ZLIB_INTERNAL for fill_window_sse.c to use
 - INSERT_STRING macro was made a function, insert_string() and an implementation using CRC instruction added
 - some crc funcionality moved into crc32.c
 
 Update to zlib-1.2.8, generate a third patch which includes the jtkukunas optimisations. We may merge some more from jtkukunas branch later.
 Currently we upgrade to madler's version 1.2.8,merged SIMD optimisation and
 some other changes above.
 The step as follows:
 1.download a clean madler zlib from github.
-2.apply google.patch, mixed.patch, simd.patch sequencely.
+2.apply google.patch, simd.patch sequencely.
 3.update these patches.