Don't explicitly list each component-target

I made a mistake while reading the Posix spec. In fact, the implicit
prerequisite imposed by the .c.o-rule is evaluated as expected, even if
the .c is not given in the target rule.

This partially reverts 0efd64ffaa.

Makefile

@@ -30,27 +30,7 @@ COM =\
 
 all: slstatus
 
-components/battery.o: components/battery.c config.mk $(REQ:=.h)
+$(COM:=.o): config.mk $(REQ:=.h)
-components/cpu.o: components/cpu.c config.mk $(REQ:=.h)
-components/datetime.o: components/datetime.c config.mk $(REQ:=.h)
-components/disk.o: components/disk.c config.mk $(REQ:=.h)
-components/entropy.o: components/entropy.c config.mk $(REQ:=.h)
-components/hostname.o: components/hostname.c config.mk $(REQ:=.h)
-components/ip.o: components/ip.c config.mk $(REQ:=.h)
-components/kernel_release.o: components/kernel_release.c config.mk $(REQ:=.h)
-components/keyboard_indicators.o: components/keyboard_indicators.c config.mk $(REQ:=.h)
-components/keymap.o: components/keymap.c config.mk $(REQ:=.h)
-components/load_avg.o: components/load_avg.c config.mk $(REQ:=.h)
-components/netspeeds.o: components/netspeeds.c config.mk $(REQ:=.h)
-components/num_files.o: components/num_files.c config.mk $(REQ:=.h)
-components/ram.o: components/ram.c config.mk $(REQ:=.h)
-components/run_command.o: components/run_command.c config.mk $(REQ:=.h)
-components/swap.o: components/swap.c config.mk $(REQ:=.h)
-components/temperature.o: components/temperature.c config.mk $(REQ:=.h)
-components/uptime.o: components/uptime.c config.mk $(REQ:=.h)
-components/user.o: components/user.c config.mk $(REQ:=.h)
-components/volume.o: components/volume.c config.mk $(REQ:=.h)
-components/wifi.o: components/wifi.c config.mk $(REQ:=.h)
 slstatus.o: slstatus.c slstatus.h arg.h config.h config.mk $(REQ:=.h)
 
 .c.o: