examples: remove unused Makefile

This Makefile isn't used anymore and probably won't work anyway.
Remove it in favor of the existing CMake build instructions.

examples/network/Makefile

-default: all
-
-CC = gcc
-CFLAGS += -g
-CFLAGS += -I../../include
-LDFLAGS += -L../../build -L../..
-LIBRARIES += -lgit2 -lpthread
-
-OBJECTS = \
-  git2.o \
-  ls-remote.o \
-  fetch.o \
-  clone.o \
-  index-pack.o \
-  common.o
-
-all: $(OBJECTS)
-	$(CC) $(CFLAGS) $(LDFLAGS) -o git2 $(OBJECTS) $(LIBRARIES)
-
-clean:
-	$(RM) $(OBJECTS)
-	$(RM) git2