starboard/types.h: Remove some unused types (#4168)

As said, kSb(U)Int8(Min|Max) are not used anywhere [1]. This CL removes
them. Verified bya local x64x11 build.

[1]
https://source.corp.google.com/h/lbshell-internal/cobalt_src/+/COBALT:starboard/types.h?q=kSb.%3FInt(8)&ss=h%2Flbshell-internal%2Fcobalt_src%2F%2B%2Frefs%2Fheads%2FCOBALT

b/366064934

starboard/types.h

@@ -57,10 +57,6 @@ typedef int64_t ssize_t;
 
 // Simulate needed portions of limits.h for platforms that don't provide it.
 
-static const int8_t kSbInt8Min = ((int8_t)0x80);
-static const int8_t kSbInt8Max = ((int8_t)0x7F);
-static const uint8_t kSbUInt8Max = ((uint8_t)0xFF);
-
 static const int16_t kSbInt16Min = ((int16_t)0x8000);
 static const int16_t kSbInt16Max = ((int16_t)0x7FFF);
 static const uint16_t kSbUInt16Max = ((uint16_t)0xFFFF);