shearwater: remove stale remnants of manual string interface code

Minimize unnecessary differences with Jef's upstream code.

The shearwater parser uses the generif field-cache code, and doesn't
need to have the snprintf workarounds for MSC, or include stdio.h etc.
The field-cache code takes care of this.

[ To be precise: the field-cache code _should_ have taken care of this,
  but didn't: it used 'memcpy()' in a macro, but didn't include the
  required header. Removing it from the shearwater code exposed this
  issue with the field-cache header, and this fixes that ]

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

src/field-cache.h

@@ -1,3 +1,5 @@
+#include <string.h>
+
 #define MAXGASES 16
 #define MAXSTRINGS 32
 

src/shearwater_predator_parser.c

@@ -20,13 +20,6 @@
  */
 
 #include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
-#include <stdarg.h>
-
-#ifdef _MSC_VER
-#define snprintf _snprintf
-#endif
 
 #include <libdivecomputer/units.h>