[LibOS] Eliminate level variable from makefiles

LibOS/shim/test/benchmark/Makefile

@@ -4,7 +4,6 @@ cxx_executables = $(patsubst %.cpp,%,$(wildcard *.cpp))
 target = $(c_executables) $(cxx_executables) \
 	  manifest
 
-level = ../
 include ../../../../Makefile.configs
 include ../../../../Makefile.rules
 include ../Makefile.Test

LibOS/shim/test/inline/Makefile

@@ -7,7 +7,6 @@ target = $(c_executables) $(cxx_executables) manifest
 .PHONY: default
 default: all
 
-level = ../
 include ../../../../Makefile.configs
 include ../../../../Makefile.rules
 include ../Makefile.Test

LibOS/shim/test/native/Makefile

@@ -5,7 +5,6 @@ manifests = $(patsubst %.template,%,$(wildcard *.manifest.template)) manifest
 exec_target = $(c_executables) $(cxx_executables) ls.manifest
 target = $(exec_target) $(manifests)
 
-level = ../
 include ../../../../Makefile.configs
 include ../../../../Makefile.rules
 include ../Makefile.Test

LibOS/shim/test/regression/Makefile

@@ -10,7 +10,6 @@ clean-extra += clean-tmp
 .PHONY: default
 default: all
 
-level = ../
 include ../../../../Makefile.configs
 include ../../../../Makefile.rules
 include ../Makefile.Test