Remove unnecessary tests for -plugin

Author: tuliom

lld/test/ELF/plugin.test

@@ -1,20 +1,10 @@
 RUN: not ld.lld -plugin %S/Inputs/plugin.so  2>&1 | FileCheck %s
-RUN: not ld.lld -plugin=%S/Inputs/plugin.so  2>&1 | FileCheck %s
-RUN: not ld.lld --plugin %S/Inputs/plugin.so 2>&1 | FileCheck %s
 RUN: not ld.lld --plugin=%S/Inputs/plugin.so 2>&1 | FileCheck %s
 
-RUN: cd %S
-RUN: not ld.lld -plugin Inputs/plugin.so  2>&1 | FileCheck %s
-RUN: not ld.lld -plugin=Inputs/plugin.so  2>&1 | FileCheck %s
-RUN: not ld.lld --plugin Inputs/plugin.so 2>&1 | FileCheck %s
-RUN: not ld.lld --plugin=Inputs/plugin.so 2>&1 | FileCheck %s
-
 CHECK: no input files
 CHECK-NOT: unknown argument
 
 RUN: not ld.lld -plugin foo  2>&1 | FileCheck --check-prefix=MISSING %s
-RUN: not ld.lld -plugin=foo  2>&1 | FileCheck --check-prefix=MISSING %s
-RUN: not ld.lld --plugin foo 2>&1 | FileCheck --check-prefix=MISSING %s
 RUN: not ld.lld --plugin=foo 2>&1 | FileCheck --check-prefix=MISSING %s
 
 MISSING: Cannot find plugin foo