Use external/mime-support's mime.types rather than libcore's copy.

Libcore was carrying a copy of mime.types that is now also present
in external/mime-support, and exposed through a filegroup in another
CL in this CL topic. Because external/mime-support's filegroup
carries the file in the root level rather than in the libcore/net/
subdirectory, this CL updates MimeMap.java accordingly.

libcore's mime.types and the associated README are now redundant,
so this CL drops them.

Bug: 135431432
Test: Checked that libcore's and external/mime-support's mime.types
      were exactly identical before this CL:
 diff {libcore/luni/src/main/java/libcore/net,external/mime-support}/mime.types

Test: atest CtsLibcoreTestCases:libcore.libcore.net.MimeMapTest

Change-Id: I632d2977f6588d92177cf059d3c048e07c38f341
4 files changed